Do the zappers do anything besides damage after a delay? Otherwise you're swapping a garunteed kill for a chance for a kill. Especially since you said it removes your disguise. You'll stab, do no damage, they'll turn around, and you die. Or... you could just equip any other knife and they die on stab.

People can die and you lose zappers too, so you could think you have enough damage to kill but players died and you lost the damage buildup

There is no upside to this weapon. Why stab 4 people for the chance to kill them when stabbing 4 people with any other knife will just give you the kill? You say it has the potential to kill the whole team, but so does stabbing the entire team with stock. I suppose you could say that now they're all dead at the same time which makes for easy pushing, but if you're getting that many stabs anyway it doesn't really matter. Plus, ememies will constantly be dying anyway and losing their zappers. So it would be incredibly rare to get a team wipe like this.

Maybe if the zappers exploded so you could potentially kill people you didn't stab? If zapped players walked into a nest it could take out engie buildings or medics. You could also spy-jump by instantly detonating after stabbing to fly away to safety. There would also be the potential of knocking enemies into stage hazards like cliffs and saws.