I bought a couple extra capacity Triple K 1911 mags back in the 90s. The first one that I used had the feed lips straighten out and let all of the ammo shoot out of the open ejection port. Never used the second and never bought another.

I haven't had a problem with any ProMag. YMMV.

A magazine is pretty simple and someone else has done all the heavy lifting on design. How difficult should it be to copy one?