The chinese made some perfect knock-offs of USGI 20rd magazines. USGI have a 3 letter contractor identifier on their long edge, Chinese do not. Both have spot welded mag catches.
USGI or Chinese, they are perfect. These are universally parkerized, although you may find refinished ones that are painted or otherwise coated.
All others (domestic aftermarket) are crap. Yes, some work, but many do not. They are identified, in most part, by their black glossy paint and stamped, not welded, mag catches.