I bought 5 of them, took a couple apart and found that the spring was put in backwards in three of the five (spring should be level on top and pointing forward... If that makes sense). I added a little graphite lube (its like 2.99 at ace for enough to lube 1,000 magazines).
They seem to work just fine, I did need to trim a little off bottom side of the rear catch for them to lock in.
Avoid dropping them or really beating them hard and they should be ok.
Oh I plastic welded 2 together and made a 60 for bumpfiring
http://www.youtube.com/watch?v=jmQK360y9QI
Best price I can find for non promag 5.45x39 magazine is at kvar.
http://www.k-var.com/shop/product.ph...cat=248&page=1