In comments, several people said that they weren't comfortable with the idea; because their general concept of a "safe" carry trigger, is a 4lb trigger weight; and Apex themselves (basically for liability reasons) insist the trigger kit is for competition use only.
A four pound or heavier trigger pull for carry guns is the conventional wisdom around the gun world; but it seems everyone has a different explanation as to why... if they have an explanation at all, other than received wisdom.
The "lore" is that 4lbs is the point where you won't accidentally trip the sear if you put your finger on the trigger when gripping the weapon, or moving around.
Unfortunately, that's a myth; and a dangerous one.
In actuality, the trigger weight that will prevent most negligent discharges under normal conditions (never mind under great stress) is MUCH higher. Something like 12lb to 16lb in fact (several studies have been done over the years, and their conclusions have varied, from under 10lb under "normal" conditions, to well over 20lb under high stress).
Under high stress, reflexive or sympathetic gripping, can be extremely powerful.
Let me explain what that means.
Reflexive motions, are motions that happen involuntarily, in response to stimulus. They are "reflexes".
Sympathetic motions are a particular type of reflexive motion that occurs in one part of the body, when we move or perform an action with another part.
Our grip (the relevant bodily function to handling and actuating the trigger on a firearm), is subject to both sympathetic motion, and other types of reflexive motion.
When you squeeze something with your left hand, your right hand will tend to squeeze slightly, involuntarily, in response (actually, if you are left handed, the right hand will tend to respond quite strongly, and vice verse. The dominant hand more strongly influences the off hand). Unless you are actively looking out for this and attempting to stop it, you simply can't... and even then, you often can't stop it entirely. It's a twitch response.
That's called a sympathetic contraction, and it's the proximate cause of a lot of folks negligently discharging their firearms (the true cause is poor trigger discipline; but even very well trained people can and do screw up sometimes, through complacency, or under great stress... I speak from experience).
Unfortunately, a lot of people develop the very bad habit of lightly resting their finger on the side, or face, of the trigger; or of putting their finger inside the trigger guard. Even if your finger isn't on the trigger, if it's inside the trigger guard, sympathetic (or other reflexive) motion can cause you to actuate the trigger unintentionally, causing a negligent discharge.
The other type of reflexive motion I'm going to address is also the proximate cause of a lot of negligent discharges... In particular, a lot of cops have shot themselves while chasing suspects because of it.
If you stumble, lose your balance, or fall, while holding something in your hand, you WILL grip that object VERY hard, with all your fingers; and you will tend to try to bring the object in close to your body. It's called reflexive contraction, and you CAN NOT STOP IT.
Literally thousands of tests have been done on this; and even if you are prepared to fall, it's simply not possible to prevent yourself from gripping hard when you fall with something gripped in your hand; unless, as you notice you are falling (IF you notice you are falling), you deliberately discard the item in your hand (or unless you train to do so for tens of thousands of repetitions, creating new muscle memory. No-one sane is going to do that).
How many people are going to deliberately toss their gun out of their hands when they fall?
Unless your finger is indexed firmly outside the trigger guard, and unable to slip into the trigger guard under strong reflexive motion; there's a pretty good chance that you're going to unintentionally actuate the trigger when these reflexive motions come into play.
Studies have been done many times over the years, and the results are inconsistent; but the general consensus is that an "average" subject will tend to grip with a range of between 20lb and 40lbs of force when reflexive motion under stress comes into play; and the higher the stress they are under at the time, the more force they will grip with.
I think we can agree, having to draw your firearm defensively would qualify as a high stress situation.
That said, no-one would accept a 40lb trigger pull on any normal gun. Hell, most people wouldn't even be able to pull it unless they WERE under extreme stress (I am a very large man, who regularly does grip exercises as physical therapy; and although I CAN pull 40lb with my index finger, I wouldn't want to do it very often. Or 20lb for that matter).
You design for the common case, not for the extreme edges; and you design to balance considerations. One consideration in trigger pull weight is comfort, another is accuracy; and unfortunately, these days the one given the most weight, is legal liability.
In the common case, a 10lb to 20lb trigger, will keep someone with poor trigger discipline, from negligently discharging their weapon during the draw cycle, or while moving about with the weapon on the range.
Sadly, this will not keep the firearms manufacturer or police department from being sued; but it will generally mean the manufacturer or police department won't lose because they had too light a trigger.
This liability issue is why the Glock New York II trigger (designed for the NYPD) is a nominal 11.5-12lb weight.
An aside: Actually, in most guns, it isn't; or even close to it. It varies from between 10lb and 14lb at the face of the trigger; because of inconsistencies in spring tension, pistol wear, slight differences in the connector angles, and differences in friction of the mating surfaces.
Also, trigger weight measurement will vary based on where on the trigger the measurement is taken, and the design of the trigger. Tilting triggers like those in Glocks and S&W revolvers, have much more leverage at the trigger tip than the face; but people squeeze the trigger from the face).
The New York trigger was designed in response to officers (many of them transitioning from S&W revolvers), not being used to the much lighter weight of the standard Glock trigger, and negligently discharging their firearms. In response, Glock just made their triggers as heavy as the DA trigger pull of the departments old S&W revolvers; which were nominally between 11 and 12lbs.
The negligent discharge issue is also why "traditional" double action revolver trigger pulls are at around a 12lb standard (lately they've been going up. Current S&W production revolvers run something like 16-18lbs), and why military arms were often designed to have 12lb triggers etc...
In fact, I believe that number was arrived at during the adoption of a modified version of the Smith & Wesson model 1889 hand ejector, as the S&W military and police revolver, in 1899; but I believe the 11-12lb nominal DA trigger pull of the revolver, was simply the result of a series of manufacturing decision, that had the happy accident of reducing the impact of private dumbass's bad firearms habits.
At any rate, like most things, it became the "Traditional" revolver trigger weight by an accidental and coincidental combination of factors; but once that was established as the standard, people resisted or rejected any variation from it. Millions of soldiers and policemen were trained on revolvers with 12lb double action trigger pulls for decades; and that's the way they "should" be.
The 4lb carry trigger on semi-auto handguns has a similar story.
Really, the 4lb number came about because of 1911s, small metal trigger parts, gunsmiths, and bubbas.
4lbs, is about the lowest you can take the trigger pull on a stock 30s through 70s manufacture 1911, without having to replace the trigger parts with higher quality, lighter weight, better heat treated pieces that have never had any stoning done on them; and still have the gun be "safe" (actually, a safe and clean 4lbs is pushing it on a lot of guns, but 4.5lbs is doable on almost any 1911).
By "safe", I mean that the pistol won't have hammer pushoff (where you can push the hammer forward off the sear), hammer follow (where the hammer follows the slide forward, or falls forward off the sear when the slide locks into battery), trigger doubling (where the inertia of the trigger -or the trigger and your finger- under recoil causes the sear to trip), or runaway (where the disconnector fails to cause the sear to reset); under heavy recoil.
4lbs is also about the lightest a "bubba", without the proper tools and fixtures, can get a 1911 trigger with freehand stoning; and not have it be TOO dangerous. Frankly, part of the whole 4lbs thing, is what one might consider "defensive disinformation"; in that if the bubbas got the received wisdom that they could get to 4lbs but anything lower was likely to kill somebody, maybe they wouldn't be so stupid and screw up their (and other peoples) guns so much trying to go lighter (in which, it had mixed success).
An important note: As I have said here many times before, never let someone who isn't an expert, with proper tools, training, and experience, work on your firearms, ESPECIALLY your triggers; including yourself. No-one who doesn't know exactly what they are doing, and have the right tools to do it, should ever work on a firearms trigger.With an ultralight trigger, ultralight hammer, good springs, and good high quality trigger parts; that are properly fitted, properly stoned and polished, and properly heat treated; it's certainly possible to get a much lighter trigger in a 1911 and still be mechanically safe.
You can actually get down to less than 2lbs (if you use VERY high quality parts, and replace them frequently) and be mechanically safe; but that discounts human factors (also, the parts will have a much shorter service life).
Anything under 3lbs on a short pull single stage trigger (like a 1911), and I worry about inertia and reflexive motion causing doubling under heavy recoil; even if you are extremely well trained in resetting and getting off the trigger (I speak from experience).
Some competitive shooters have their race guns set up with as light as 1.2lb triggers, but those are highly tuned guns, highly trained shooters, and they replace the parts of the gun LONG before they wear out.... and frankly, I still think it's a silly idea.
There are some folks who brag about 12oz triggers on 1911s; but for one, I've never see a 1911 trigger lighter than 18oz that I would consider safe, and honestly, I really don't see the point.
Anything less than about 3lbs or so isn't going to make a bit of difference in competitive accuracy (it's basically a bragging rights issue). It's really the clean break, without any stacking or creep that's more important, and going so light actually makes it harder to get that break perfect. I'd rather have a 6lb trigger with a perfect break, than a 2lb trigger with anything less than a perfect break (and honestly, with a perfect break, that 6lb pull is going to feel, subjectively, lighter than the 2lb without it).
Plus, the parts wear out so much faster (particularly for a competitive shooter, who may shoot 50,000 rounds a year), you're having to constantly do new triggers; and you're always carrying extra risk of getting a procedural or technical (because, as I said, even a well trained shooter can screw up).
Other firearms designs have their own limitations.
An N-Frame Smith and Wesson revolver, with a good smith, can get down to about a 7lb DA trigger pull and still be reliable with most ammo (though a trigger under 8lbs may have a problem with hard primers).
That same gun can be tuned down to an under 1lb single action trigger; but I recommend against it because the trigger parts will wear down very quickly, and the hammer may push off if hit hard, or dropped. My personal 625 has an SA pull of just under 2lbs, and it breaks with a hard wish.
With a Glock, the limits are determined by the geometry of the transfer bar, striker, trigger connector, the springs in the trigger system, and overall friction in the trigger system.
The practical limit on a 100% safe and reliable, and reasonably crisp, trigger for a Glock is about 2.5-3lbs or just a bit under (every gun is a little bit different); and most other striker fired auto pistols are somewhere around there as well.
Because the Glock in particular has a long travel trigger, with a semi-cocked striker (with the trigger in its neutral position, the striker doesn't have enough energy to ignite a primer, even if it falls without a trigger pull); the weight of the trigger itself isn't much of a safety factor.
The important thing is to have sufficient engagement between the components, and sufficient spring pressure; that inertia, metal fatigue, or small pieces of grit, wouldn't cause doubling (or worse, a runaway) under heavy recoil.
Also, with Glocks (and again, most other striker fired auto pistols), very light trigger weights can actually feel worse than heavier weights; because the very light springs required, make the trigger feel "soft", "mushy", or "spongy" rather than crisp. This can actually hurt accuracy (as I said above, the break is more important than the weight).
My personal opinion, is that any trigger that is mechanically safe and reliable; is TECHNICALLY suitable for carry.
The real problem though, isn't technical, it's legal.
A 4lb or higher trigger weight, is the conventional wisdom and "industry standard" for a carry trigger.
If you deliberately act to carry a firearm with a trigger lighter than that (particularly if it's against the manufacturers strict recommendation), then you are taking on a huge potential legal liability in the event you have to use your firearm defensively.
First of course, is being portrayed as having an "unsafe" modification, or "hair trigger" in the event of a jury trial.
As to how much impact this will have... Ask Harold Fish. He carried a modified 10mm, and the prosecutors successfully argued that because he did so (both the light trigger, and the fact that he carried such a powerful round) he was "looking to shoot someone".
Most of the time, juries aren't that stupid (prosecutors on the other hand...), but sometimes... That said, it doesn't stop me from carrying my 10mm 1911 (with a 3lb 12oz trigger by the by).
Second, most shooters are not used to such light triggers. If another shooter picks up your gun, and has poor trigger discipline; with a very light trigger, even when you warn them, it's entirely possible they may ND during draw or presentation.
I've had this happen with several different shooters, and several of my guns (including those with over 4lb triggers); mostly Glock shooters who weren't used to 1911s.
Finally, there's you. Are YOU, personally, safe with a 4lb or lighter trigger.
If you aren't well trained, and well practiced (or, even if you are, and your fingers just aren't that sensitive), it can be VERY easy to unintentionally trip a very light trigger.
A lot of folks assume that 5lbs is a fair bit of weight; after all lots of people exercise with 5lb dumbbells. With your grip though, it's different.
I'm a guitar player and a bass player. Finger strength is rather important to folks who do that. I use a 50lb whole hand grip exerciser, and an "extra heavy" Gripmaster pro five finger exerciser, with 11lb of tension on each finger; and I feel barely any resistance to my index finger squeeze.
Even my wife, who has comparatively little grip strength, can squeeze the 11lb index finger pad easily enough, and she has no problem with the trigger pull on my J-Frame 340pd ( so it's not actually a matter of trigger finger strength.
Some folks can't feel any difference between a 2lb trigger, and a 6lbs trigger, simply because their proprioceptive sense just isn't fine enough, or isn't trained enough.
And of course, there's simply a matter of what you're used to, and what you're comfortable with. 4lbs of trigger weight seems EXTREMELY light, when you're used to 6 or 7 or 12lbs; never mind 3lbs. Also, most people are used to some takeup, some creep, and some stacking in their triggers. When presented with a trigger that has none of these things (or very little), even if the trigger is hev peoples "surprise break" can be more like a "whoa, how the hell did that thing go off" trigger break.
So, if you want a lighter than a 4lb trigger, I'm perfectly OK with it, and it's most likely perfectly mechanically safe; so long as you are personally safe, and comfortable with it, and so long as you accept the potential liability issue.