I've got the RRA 10.5" upper with the RRA integral magwell lower. It has been flawless with C Products Grey Follower Mags. I tried the new red follower C Products mags & they jammed 3 rounds in 10. The gun was Jam-O-Matic during break in but that went away after a hundred rounds & lots of lubrication.
I'd get another RRA upper without hesitation. I used to have the Olympic Glock 9mm AR but that was a malfunctioning P.O.S. No amount of gunsmithing could make it function properly.