I've built 2 of these lowers into Carbines. The first one went together easy as pie, and has been running like a raped ape.
The second, had a slight machining error on it, and had to be rectified with a jewellers file. Took about 40 minutes going nice and slow.
The glock mags all fit fine. Drop free. No hassle. The Kahn Korean surplus ones don't fit worth a crap. They also are a slight bit short front to back so some 9mm rounds don't fit well. I decided to can the Kahn's, instead of working open the mag wells to work with mags that I find suspect anyway.
The anodizing isn't the best. It's not mil-spec and is starting to purple on me. I use the rifle a lot and it spends a lot of time on the range, at 3 gun matches, etc. It spends a fair amount of time outside in the sun. The mag release is worse than the lower. I will duracoat this gun eventually, but right now it's just plain FUN to shoot. It's cheap to load 9mm which was my motivation for making this gun in the first place. It doesn't have a bolt hold open, which isn't such a big deal, but it would be nice.
The ejector is held in with 2 set screws. It works fine, but if you get aggressive with a magazine, slapping it home you may tilt the ejector and then it will rub on the bolt carrier. I decided to combat this extractor tilt by drilling a divot into the ejector to allow the front most set screw to countersink about .010. This essentially "locks" the ejector to keep it from tilting if the mag is inserted forcefully, as often happens in 3 gun stages.
I did use a Rock River Arms Upper, with the bolt narrowed for the single feed Glock Mags. I also had the bolt ramped to relieve stress on the hammer pin. This work was done at ADCO.
I like the rifle so much, I SBR'd it.