I've had my Osprey gas piston system installed for a little less than a year. This was my first build and I decided piston was the way to go. I love that it keeps the gun nice and clean and it is rock solid reliable. Zero failures due to the gas system. And install was easy, even for a noob like me. Took me way more than the 4 minutes they like to brag about, but still pretty straightforward.
But the downside for me is that almost nobody make a free float handquard that will work without alterations. And I hate the delta ring/forend cap method of handguard attachment. The handguards that come with are junk, so I'm using the Magpul forend. Better, but not what I want. Osprey Defense was bought out some time back. And now their web site sucks. No support whatsoever, and no new support from handguard makers either. Unless directions change, I think the Osprey will become a footnote in AR piston history.
If I was to do it over again, I wouldn't buy it. I wish I had bought the Adams Arms unit instead. Maybe the design isn't as good, but they got the head start, and they continue to have better support all around.
-- gr8whyt