C Products mags are fine if you test every single one twice with a full load of ammo. This is based on personal experience, with a lot of their mags and a lot of AR mags from other manufacturers. Their quality control is poor and as far as I can tell hasn't improved. Witness the debacle with their recent introduction of 30 rd x39 AR mags. I have probably two dozen of their mags (all .223, mix of aluminum and stainless steel) and when I bought I foolishly assumed they would all work, so I only tested a couple. Wrong! Now as I try to use more of that same batch I find a lot that either don't fit or don't function. Again, you must test each mag they make.
OTOH, I have not had similar issues with nearly any other brand of AR mag except Promag. My experience has been great with Cammenga, DPMS, and NHMTG (note: I think the DPMS mags are made either by NHMTG or Okay Industries). The Magpul Pmags are also great, though I bought early enough that I got one of the batches with a molding issue that made them unreliable in feeding. Magpul had identified this issue and offered a really no-hassle exchange program to replace the defective and possibly defective mags (anything with that batch code, some of which probably did work fine).
C Products customer service is decent and if you get lemons they will likely replace them with no hassle. But you will need to spend about $30 worth of ammo to adequately test each $10 mag.