I've used them for years and as long as the spring and follower are good the unit is GTG.
That said, I've had the best luck with C-Products brand (black teflon coated) at about $10 each. AIM Surplus has quality aluminum mags. Stay away from any AR magazine (metal or plastic) made by USA Brand/ProMag/Thermold as they are generally junk.
While I do own and use a number of Magpul Pmags, their torture-testing is pretty unrealisitc for those of us in a non-combat world.