Anyone w/ some engineering knowledge understands AR15 was not designed for piston cause carrier key location piston contact creates bolt carrier tilt due non-center mass pivot point, buffer recoil spring not inline w/ piston action movement.
Other piston designs like M1, M1A, AKs, FN-Scar, HK G36s do not have this problem cause recoil spring & piston action are inline. Bandaid solution to minimize excessive wear for the piston design in ARs are oversized bolt's rear rails (tilt issue),
spring loaded bolt (premature unlocking issue).
I have noticed no one has mention this yet, AKs and M1A pistons design are very reliable due their piston action area were enclosed, minimal dirt & mud intrusion and AK's loose tolerance design,
but piston ARs w/ rail system w/ many vents holes do allow dirt & mud to enter piston action area when operators are crawling thru mud or very harsh enviroments, this may or may not be a problem.
Let's all admit that introducing more moving parts is a potential guarantee for more breakage compared to less moving parts. I am not bashing piston ARs, just pointing out valid facts.
But hey, you you like pistons ARs for extra money, go for it, don't worry what other nay sayers think...