If I have any mags that malfunction or don't perform, I destroy them. A lot of people will sell them, which is shitty, but I won't do that. Happens in commieland, I know for a fact.
Most polymer mags outside of Mil use, tend to perform just fine. People don't get them as dirty or abuse the crap out of them. The biggest thing I've seen is loading them up to max and keeping them loaded a long time. Doesn't really hurt the springs but what it does do is deform or bulge the top...that's why magpul has that lid. Cracks are another common thing I see...usually because a loaded mag falls out of a safe or something or someone realized he can shove just one or two more rounds in a mag and thinks, "wow, I have a 32 round Mag", which is not the case.
Magpuls are the only polymer mags that can be procured...like as an approved accessory; may have changed in the last few years but I don't follow weapons acquisitions much any more. Some of the others might have an NSN but you can get an NSN for an acorn if you know the process. I don't think Thermold are GI anymore.