I have several of the the Z3s (4-12X50) and not one has ever lost zero. They are very light, great glass, a joy to look through, and fragile. I also own several of the Z6 line and a few Z5s. They are all wonderful. Never had a problem.
However, I would never purchase another Swaro scope. Today I buy NF and want to try a SB Polar. As beautiful as Swaro is to look through and carry they are set it and forget it scopes (excluding X5, that is a tank!) that will not hold up to rough use. I own several Swaros with dents in the tube assemblies. Lightweight equal thin tube and you can see it on mine.
If you do buy the Z3 best of luck and enjoy the crisp optics!