I have a ZA5 4-20x50, I like it a lot. I don't have the problems with the dials that others have had, mine feel pretty positive and it seems to track well, perfect so far in fact. I have it on a mid range .25/06 and use the BDC reticle. Zeroed at 300 yards my hold points are dead on at 350, 400 and 500 is the top of the bottom post all at 20x. The glass is great and compares favorably with my MK4. Mine was an open box special from Cameraland so I got it for considerably less than a new one but if I were in the market I would pay full price based on my experience with this one.
Bob