My agency bought a pile of the Brownells mags and had nothing but issues with them. feeding issues mostly.
P-mags are the industry standard these days and I'll be honest, it's hard to beat them. C-products (especially the stainless steel mags with magpul followers) have been outstanding as well, I just bought 18 for my OBR .308 and I hope they run as well as the 5.56 mags do.
Just keep in mind, AR mags were originally meant to be disposable, it's the weakest link in the system. Buy quality mags but don't get married to them, when they start to **** up, throw them out! Or mark them and keep them for training.