They were on sale through sportsmawarehouse for under 2k. Wish I could have afforded it. They say an adjustable gas block is better, but that's mainly if you're running the gun with a suppressor or running it dirty.
I only run brass, so I would have been golden.
Less room for error with a mid/full lenth gas system, as most high ends are adjustable gas block, which have their benefits. They're worth the extra cash if you can't clean your rifle often enough