My ATI came with a ACT mag and 3 stainless Colt(aka CheckMate)mags. Didn't even bother with the ACT because of all the bad reports I'd read about them. The 8 round Colt mags with the CMF(CheckMate Follower) ran like a charm. Made the mistake of selling them after I bought 5 Metalform mags, all of which had weak springs.. Sent them back and bought 3, 7 round CheckMate mags with Hybrid feed lips and the CMF and they're running like a champ. At $17 bucks a mag I've found the ones my gun likes and they don't break the bank.
*Glock G19 Gen3, RTF2*