I have some promags that work fine and others that are junk. I only use them for range use. Mecgar is about the only aftermarket mag I trust.
As for the 3913 mags, hit the local gun stores/pawn shops and check out their used mag bins. Sometimes you can find a deal. I picked up 2 at one store for $15 each. They had one more, but I left for someone else. I had a 908, but after buying a 3913, I went back to see if the other mag was still there, got it for $10 out the door this time. Some of these stores really don't know what they have. Be patient and keep your eyes peeled, you may run across a deal.
Rosewood