just before the obama panic of 09, gas piston conversions were all the rage in the AR-15 community.
personally i don't see any huge need being addressed with a gas piston conversion. what a gas piston conversion usually does is make the AR-15 into a ar-180. most conversions are expensive enough that that money looks to be better spent on a rifle that is designed with a piston ie AK/ar-180 ans so on. the exception would be this $250 set up. still not cheap--but reaching towards a more economic solution.
i happen to have a ar-180 and a bushmaster m-17s bull-pup which run the same type of gas piston system. they are good systems and reliable. they don't get as much dirt in the chamber/bolt area as the AR but they still get dirty. the ar-180 and m-17s are heavy for a 5.56-- so a gas piston adds more weight.
a SBR ar-15 with a 1o inch or 11inch barrel could really benifit from the gas-piston system i would recon.
anyways--any thoughts on the CFS kit???AR15/M16 Gas Piston Conversion Kit Part #AR-GASPISTON