With all due respect, a problem with it not holding zero is likely not a problem common to the sight. Not holding zero can be a any of several issues, especially loose mounting screws or insufficient torque on the mount screws.
I'd suggest you double checking the mount system for tightness/security before condemning the sight itself. A 'really competent gun smith' can usually 'feel' an appropriate torque on a mount screw, at least close enough to keep it tight. The rest of us usually need a little help in the way of a good torque sensing screw driver or a 'really competent gun smith'.