At least one Reviewer seems to know what he is talking about though...
"I found this toothbrush okish, my girlfriend has the proper Braun sonic costing more and I thought I was going to get the same performance since there is no mention of the vitality model being a 'lesser' model sonically, however it is considerably less powerful than the 'complete' model and I feel conned to a degree. This is maybe only just better than a manual toothbrush. "
I have the Complete model that the reviewer had tried and it produces comparable results to the Professional brushes with the round heads. He seems to be saying the Vitality range is a lesser model prducing lesser results. Mine was £30 at the time and seemingly well worth the extra where you teeth are concerned. Tesco Direct have the brush head at 2 for £2.47
http://direct.tesco.com/q/R.100-3248.aspx which is a real bargain....or part number 100-3248 if the link doesn't work.