Nothing but problems with the KCI glock mags I tried. I don't have any direct experience with their AR mags but I haven't heard good things.
As others said, good mags are so cheap these days why bother? Just buy Magpul if you're looking for a value, you can get them for $8 or less a piece. I personally prefer metal mags or at least metal feed lips because the polymer will stretch over time despite what anyone tells you. For 556 I like the Bravo Company mags with Magpul followers for 30's and either Brownells or Lancer for 20's.
There are other metal mags like C products, ASC, and OKAY but IMO the BCM, Brownells, and Lancer mags are higher quality. The finish (especially BCM) is fantastic and there's never any burrs or sharp edges on the lips which makes them feed buttery smooth.