Sorry, but I would disagree...I have a ZH Gen 2 that was a total lemon until I came here and tried all the different fixes to finally get it to work reliably (changing mag springs [Wolff], adding grip tape, running over 200 rounds through it to insure 'break-in'). I was happy that it finally came around and started to be dependable...I would have never bought another if it hadn't.
I was actually surprised that the ZK worked so well...but then again, I wonder if I used a normal, non-Wolff spring mag in it if those pesky failure to feed would appear. I'll have to check if I have any that I haven't 'fixed'.