The Serpa holster has known inherent issues with its design:
#1) Poor design of trigger finger button to release gun from retention. With proper trigger finger discipline and training this is not an issue, but it is non the less a poor design.
The design lends itself to the motion of riding your trigger finger into the trigger guard- operator error yes, but the design makes it much easier to do this and for the operator to have an AD.
#2) Small particles can get stuck in the release mechanism causing your firearm to be locked into place. Another poor design choice, especially for those in the outdoors who are around a lot of dirt/twigs/outdoor debris. I have seen this happen on 3 occasions, it was a small rock fragment once and small twigs the other times. Had to disassemble in all 3 incidences.
#3) You can insert your firearm into the holster backwards and it is then locked into place until partial disassembly of the holster is conducted. Again, another issue with a poor design.
#4) The retention hood serves no purpose. A good hard yank on the gun (with the serpa button pushed) will pull the gun up and through the rubber hood without the need to deactivate the thumb latch. This retention feature is nothing but show.
#5) The screws that attach the holster to the belt loop work loose in very short order. Now, most people will occasionally check their gear and notice this kind of stuff but some won't.
#6) I've seen it time and time again where someone with a serpa at the range failed to disengage the lock, thus tugging the holster and their belt halfway up their torso. I could clearly see the most common response to this problem was being more aggressive with an inward press of the button during the drawstroke. That's a recipe for an AD.
With #3 some Serpa's do it and some don't, but it is a known issue. I know some folks will not understand why a gun would be inserted backwards at all- It's a common (and effective) means of securing the pistol when you need two hands but only have one available due to injury, etc.
Think reload, malfunction clearance, etc. While other techniques are taught in some places, your holster is always there and always ready to hold a gun regardless of your stance, position, etc.
It's also a technique that minimizes opportunity for students to cross body parts with the muzzle. Such cautions are especially prudent with basic and lowest common denominator students, and/or where training time is minimal. Using joints (behind the knee, armpit, etc), shoving the gun in the waistband, kneeling or stepping on the gun, are other alternatives. Each has its own merits and liabilities.
Shooter error magnified by a bad holster design is a recipe for an AD.
The only job your trigger finger should have is to pull the trigger. Creating a release button that can cause bad muscle memory and possible AD's is not a good idea.
If you like them, rock'em. But be aware of the issues inherent with the design.
If you're going to take a training or CCW course, email ahead of time to make sure they allow them. Most courses I have taken DO NOT allow them.
Also, many agencies have banned them from use due to the inherent issues and poor design.
For level III retention the SafariLand ALS is definitely the way to go. Yeah it is approx $80 and the Serpa $30, but you get what you pay for.
Some reading material on the SERPA:
http://lightfighter.net/eve/forums/a/tpc/f/1931084651/m/86120086563/p/3
Blackhawk Serpa CQC holster
