Fidgiegirl, it's not just theory. My DH and I have a Sonicare Elite. Two interchangeable heads that sit in a holder and just screw on to the handle. Yes, expensive. And the models of the heads are not interchangeable. I agree, so much better results than manually. I use both, using the Sonicare when I feel I need extra cleaning action. By doing that I don't have to buy new heads as often.