It's similar, but it works against non-heroes, can be activated by shooting from the front, grants firerate and scaling. But I think the cooldown should be reduced to about 8 seconds.
the item is to similar to backstab
one way to make it distinct would be to make its damage increase overtime and be able to reapply the effect before the duration runs out
for example make the cooldown 3s and the duration 4s with a base damage of 10dps with a growth of 5dps (maybe even add spirit scaling)