Exactly what it says on the tin. Adjusting the amount of resistance is easy. The counter built into the handle is useful, not really for counting reps but for making sure I'm maintaining my grip, since it'll unclick if I loosen up before relaxing completely.
It would be nice if there was a way to measure what the resistance is actually set to, something like a little print-out that says "if the distance between the handles is X cm, then it's Y kg of resistance".