I was given one of these as a Christmas gift. The bristles do not move at all, instead the whole handle/toothbrush vibrates. You have to use just about as much effort to brush as a standard toothbrush, because otherwise your teeth feel just as slimy as they were to begin with. I would recommend skipping this one in favor of one where the bristles move/spin on their own.
My 5 year old got a Dora one with spinning head from Colgate, and the dentist commented how clean her teeth were, and was surprised that she brushes her teeth without help.