I have only had experience with the Glock 19 versions and they were sub par. Usually won't load to capacity and 1 in 3 will randomly bind up.
Same experience, I had two of them and eventually threw them away. Especially with Glock mags, IMO it is best to spend the extra dollars to get OEM mags whenever possible. For my HK SP5, I heard the KCI mags weren't too terrible, but I forked over the extra money to buy HK ones, spending $40 extra a piece, and with zero regrets. I have no clue about their M1 mags.
I have several KCIs for my M1s and they have performed flawlessly.I hear their M1 carbine mags are decent, which makes sense considering how many of those are in Korea. However, I'm getting the impression anything else is on par with Promag.
You'd think there'd be more M1A/M14 surplus in circulation.