There are a lot of aftermarket 30-rd carbine magazines that are junk. It is a shame that scammers are marking magazines and selling as originals.
I agree, the shiny UU 30-rd carbine mags work 99.9% in my M2, I think they were made in Taiwan or Korea. They are more reliable than my original GI 30-round mags, and less expensive. I bought some at Knob Creek a few years ago for $9.00 each. I bought some similar-looking aftermarket Sten magazines from Keep Shooting.com (shiny black finish), which are far more reliable than originals. But the Sten magazines have not been available for some time.
It isn't too often that aftermarket magazines are more reliable than originals.