I have the NFA upper and lower and have no complaints. Mine is an 8" and is in a pistol form with a Shocktech Blade. The mag catch/release on mine is aluminum not polymer. I did roll the edge on the part that actually goes into the groove on the mag. That way I don't have to press the release to insert the mag. I've tried it with factory Glock 17 and 19 mags as well as Glock 33 round, Chinese import 33 round and Magpul 17 mags without a single problem.
Dan
I myself have been looking for a good build video on a budget 9 mm AR carbine build. I have searched the net & all I find is SBR style of builds for the 9 mm. I want a rifle. So if anyone has seen or found a build video with a parts list & where to buy, most places I have searched don't have anything really for the 9 mm AR platform. Thanks for all the information & help. I really want this to me my next rifle build or purchase.