I read that the reason Thermolds have a checkered past is that the Canadians decided to deviate from the plastic formula in a cost-saving move that altered the heat resistance properties of the plastic. Therefore they melted when doing full-auto mag dumps.
Now that is what I read. Similar to the "jam-o-matic" reputation AR-15's received when the US famously decided to change gunpowder recipes during Vietnam and we have all heard that story.
Now personally I don't trust anything that shits where it eats. But that's just me
Apparently the Master Molder company from NC is associated with Thermold magazines. Not sure how... perhaps they make (made?) them. I am going from memory and I'm at work so I can't really look this stuff up to verify. I say that only to say that I've had VERY good luck with current-production Master Molder AK magazines, FWIW.