I haven't had a single stoppage or jam that I can recall. That's with about 200 rounds through it, being a mixture of Portugese mil-surp, Radway mil-surp, and some new/remanufacture American Eagle ammo. I've mostly used those alloy/alum mags but I also have one steel mag.
In one respect you could say that 200 rounds aren't enough to gauge reliability, but on the ohter hand you could say that stoppages are likely to occur when the parts are new and tight. So far, so go.