According to people who know about these things, there is only one piston system worth buying, the Hk416. And only really if you are doing a lot of full auto/suppressed.
It is the only proven system in actual serious use. All the other ones are at best proprietary, and at worst, bolt-on additions.
It is the answer to a non-existant problem, the AR system was designed as DI. If you want a piston, get a rifle that was designed from the ground up as a piston gun.
It is certainly not something you want as a first AR.
You can argue all you want that your sample of one (or maybe two) is flawless, clean, bla, bla, etc. but the experts and people who deal with bigger samples disagree. Look at who is using what, and you will see what I mean.
I believe it was Elmer Keith that said " jet engines don't have pistons, and neither do my ARs".
Regards.
Mark