I have never had a problem with aftermarket mags in my SP1 or bushmasters, never got a jam yet.
I did have problems with some cheap USA mags for a 9mm firestar so I wont buy **any** usa mags again.
I just bought a shitload of western metal AR15 mags new in the wrapper $7.00 each for 30rd, $11.00 each for 40rd. Replace the BF with GF and they run great. Cheaper than USGI, just as reliable, new teflon coated mags look better than beat up GI mags.
I never heard any bad things said about aftermarket mags (other than usa) among my friends and people I know who use them. The only downside to steel is it can dent if you really wack it on something.
I will continue to build up my stockpile of cheap aftermarket mags because they work, and they have to be cheap enough that I can pop um and drop um.
And I wouldn't touch those replacement mag bodys with a ten foot pole, #1 they cost too much, #2 great way to get your name on the ATF shit list.