I think it is a nice secondary weapon if your primary is for add clear and your secondary needs to be a single target focused dps. Holding the fire button throws the kunai really fast, so it can do monstrous single target damage if you have the incarnon charges.
edit: Because the shots home in on the head, it will always focus fire a single target until it's dead, so I don't consider it a room nuker even though it can kill groups.