For me, it is worth practicing. Play around with the different effects. Pay particular attention to the part of the helpfile which says "to provide an edge for eventual combat". Specifically, it might help to take notice of your varying degrees of success against mobs when the different darts land versus not. I consider it just another nifty piece of an assassin's toolkit, not necessarily a dealbreaker.

Edited: Oh, and it doesn't initiate combat, which is nice.