I have an Adams Arms piston retrofit kit on a DSA upper, and I have been very pleased with its performance so far. It does keep the action cleaner (not clean, but cleaner) than a DI model, and it does keep the heat out front and away from the action.
BUT...it is no more accurate or reliable than my DI ARs. I bought it just to try it out for myself...personal experience is better than internet rumour. I do not prefer it over my DI ARs, but neither do I shun it. It is just a play pretty for me, and I have played with it a lot since I bought it!
LMT, POF, Stag, S&W and CMMG are some of the makers who offer complete piston uppers. But IIRC, Adams Arms offers complete uppers now, also.
Wheelhouse #452, 10 Ring#5744, Mil Surp & MBR# 3006, ad nauseam
"By and large, the most successful riflemen were the over-mountain men of Tennessee." Richard B. LaCrosse, Jr., The Frontier Rifleman
"....the man with the rifle knows." USA AMU