Quoted:
They don't drop free from all mil spec receivers
They hang up on mag pouches
They don't fit all guns that use mil-spec M16 mags
I think they are damn good mags, but the above are serious short comings
Some answers...
The newest versions are 100% dropfree tested prior to shipping. They should drop free of any factory Colt M4 and 95% of aftermaket receivers in the market place.
The only two mainstream rifles out there that do not take stock PMags are the HK416/SA80 which both have non conforming magwells but can use the new EMags which are designed to fit. It also does not fit the FS2000 but we don't really think it is an issue. They work in the FN SCAR but will not drop free (the EMags drop free just fine) Other than than it is compatable with the majority of AR15s and systems that run an AR mag such as the SIG556, Rob XCR, MSAR AR-AUG and FN M249.
I cannot help you on the pouches part other than tell you that there are plenty of pouches that fit it and in the AR Polymer mag world the PMag is on of the more "Swelt" ones out there.