I find it best to use on defense. I have only used it as a medic so far. Just sat in the back while the other team was trying to escort the guy across the map and every time they grouped up, popped the whole group with it. It doesn't kill very fast, but it's good for disorienting/stopping a large rush of people.
The hard part to get use to is learning the arc and the timing, since you probably noticed that it's got a bit of a timer. Also funny to hit people with it and watch them get knocked down.
Just practice and you'll get the hang of it, but I don't think it's meant as a fast killing weapon. More crowd control than anything else.