Is this an item that you would say is really necessary for playing onstage, or is it more just a thing you can have if you want? From what I see they're pretty expensive, so I don't want to get one if it won't really help. But it does seem to me that it's pretty much the only way one could hope to tune up on stage, so I probably will have to get one regardless of the response. That said, what kind of pedal tuner should I get, guys?