Got my 3 in today. I'm running a 6.5 SAUM so I had to bend the feed lips out just a hair to get them to feed the larger diameter cases. That said, the material/heat treat on these is significantly better than the alpha mags I was using. No bulging, and significantly more force required to bend the lips. They feed great, very smooth. The coating on them is pretty slick. Time will tell how they work in the long run, but just getting the lips right and testing it out tonight, probably 5-10 full loads on each magazine, they're looking pretty good.
For those curious, I bent the lips so that the inside-to-inside distance on the top of the lips was about 0.410-0.415" in the rear, and right about 0.435" in the front. Gives slick function with my 6.5 SAUM. YMMV.
They drop free from my PTG dbm.
ETA: They hold 6 SAUM rounds. Alphas theoretically hold 7, but the top round feeds like shit because it's so tight, I was only ever loading 5-6 in the alphas anyway. ARC mag is about 3/8" shorter than an Alpha 10 rounder.