It's a powerful weapon, but it has lots of downsides and people who use it are just as easy to kill as they are able to kill others.
I think most of the reason people have such success with this weapon is that their opponents are not used to its speed and attack methods (quick dart in and out, or rapid succession of crazy stabs) and they are caught off guard.
If it is truly OP, then more people will start using it, and then more people will get used to going up against it, and people will adapt their playstyles and stop underestimating it.
I don't think its very OP in its own right.