My 16" M4gery and two 6.5 Grendels (20" and 24") Uppers are AR Stoner; one being completely homebuilt from AR Stoner components. It is a slick side billet upper with a blended handguard. Aside from the BCG, it has no other moving parts, like Forward Assist, or Port Cover, though the Case Deflector remains. So far, the assist and cover do not appear to be needed.
One, the 24" Grendel, broke an ejector; but that was due to running excessively hot handloads. It was replaced with a JP Enhanced 6.5 Grendel extractor.
In general, I like the product, especially like the price; and AR Stoner will be my first choice for more AR projects.
I also find that the Palmetto State Armory PA-10 and PA-15 Classic Lowers make affordable armatures upon which to upgrade.
My PA-10 is comprised one each of PSA Upper and Lower. Since function testing; it and the others above (but not the M4gery) have each been upgraded as bag riders.
Greg