I have Pmags, Emags, Lancer, U.S.G.I., and Troy, on my U.S.G.I., mostly green followers, some have updated magpul followers, I own too many to test them all, the ones I have tested have all worked.
I run Beretta mags in Berettas, Para maga in Para's. For 1911's, I run Colt or some other premium magazine. I do not care if they are stainless, blued or painted as long as they are dependable. For the AR I use USGI issue. I am still using 20 round Vietnam vintage aluminum follower 20 round mags that I think the caked mud inside is from South East Asia. They work, as do the later vintage plastic follower versions. I have NEVER called for an equipment alibi during a match do to my stuff not working. I started pistol competitions in 1980 and High power rifle in 1996. Do my mags match? Of course, they match the firearm.
Well, I've got 4 different guns that use AR-15 mags (Rock River TacOp AR, FN SCAR, FS2000, and my Alliance Armaments SABRE). I generally gravitate to PMAGs, but with the last year being so crazy, I bought more mags when I could get them a for a good price (no $70 PMAGs here). So, I have a big mix of Magpul PMAGs (Gen 2 and Gen 2, windowed and non) and EMAGs. I also have a decent number of D&H and E-Lander metal mags, because the FS2000 hates PMAGs (they are too wide to fit and I don't want to alter the mags). Plus, I have a box-full (and I mean a box-full) of Thermold 20 and 30 rounders I got for like $3 a mag, plus a couple of old beat up GI mags that I picked up at some Knob Creek or another for less than $5 per (I've had a few fail on me, so I retired the whole lot of them).
So, basically a giant mismatch. I generally maintain Magpul polymer mags for all of the 3 guns that take them (though I've mixed and matched the types there, EMAG and PMAG G2 and G3) and a mix of D&H and E-Lander for the FS2000.