I use one (and the first gen 'possum pouch' knock-off) almost exclusively with my G26 in the summer time when concealment is tricky. Somewhere I did a write-up on them, but my experiences summed up are:
pro -
- easy concealment, NEVER prints because the entire gun is covered all the time
- easy to use in a restroom, don't have to set anything down or risk dropping it when your belt is open
- comfortable, wore it for days on end walking at the NRA show last year, no issues
- very secure, can run/fight with it on and gun won't pop out (at least when working against a heavy bag, haven't spared with it on or anything)
- can draw while seated in vehicle (mostly)
cons -
- slow, draw to first hit was something like 2.5 seconds vs. 1.8 seconds out of a normal AIWB holster from concealment
- one handed draw is tricky and slow, two handed draw needs more practice too since the non-firing hand has to potentially move two things (cover shirt and the holster flap)
- feels heavy, lots of leather against you, so lots of warmth in the summer
- can hang up under a seatbelt when drawing if you've not got the belt in the right spot
So basically it's top notch carry and concealment, but way less of a 'gun fighter' rig than a regular AIWB holster. Also probably sucks when trying to use a larger pistol, I can see something like a G19 getting hung up on the draw due to the longer grip.
Also, the redesigned 'possum pouch' that they made to get around the lawsuit is a POS. Watch their videos closely, the guy always sweeps his off hand on the draw. Doesn't happen with the real urban carry since you're pulling UP instead of forward. Those statements probably make no sense without the videos.
EDIT: total aside. while on a trip with the wife I was carrying in the pouch and we went into a ranger station so I left the gun in the car but kept the holster on because the old style one requires removing your belt to get it off. we subsequently went hiking directly from there (with almost no gear, it was a mile hike on a totally groomed trail to a waterfall with 100 other tourists) and got caught in a downpour. no rain gear, no nothing so I grabbed our phones and stuck them in the pouch while we ran back to the car. we were totally soaked through, but the pouch saved the phones. wife gave me less crap about carrying after that.... even if it was the pouch and not the gun that saved the day. the pouch took almost 2 days to dry out. glock didn't rust though.