A lot of these have the "overhop" issue as standard. Replacement with a different bucking and nub sorts them out.
Ive also noticed, after working on half a dozen of them, that the hopup units tend to "creep" while fired, which is an unusual problem for mp5ks. This can be solved by taking the hopup unit and barrel out of the gun, giving the post on the hopup unit that protrudes through the slider a slight shave, and tightening the screw down. Be careful not to shave too much because it'll prevent adjustment at all, or make it very difficult.
I also think theyre a little hot for cqb, but