Review (5/5): A purchase I do not regret.............
I have used this toothbrush for 2 months now, so while I cannot really comment on subjects like longevity or reliability, I can say that it functions perfectly.
Firstly, it cleans teeth and gums SO much better than manual toothbrushes, or my one previous electric (Bausch and Lomb Interplak). An experiment that I tried that you can duplicate (if you have any interest): eat a "problem" food that usually leaves bits stuck between your teeth. For me, this means blueberries (the skins) or tuna. Brush with your manual brush. Then rinse and spit several times, until no more debris is coming out. Now floss throughly and then rinse and spit several times again. How much more debris do you get now? This is what your toothbrush did not get. Now try it again with the Oral B.
With the Oral B brush, my mouth FEELS much cleaner, and I end up with much less food left for the floss to get.
I chose the 7550 because I wanted the Oral B "3D Brushing Action" mechanism at the lowest price, and when I looked at the various models for sale, it seemed that the major difference between them (that was not just gimmicks) was the number and types of brush heads that were included with each model. I figured that since these were expendables, I would be buying more of them over the years anyway. In the end, the 7550 with the four brush heads that are included and 6 refills that I bought at the same time cost less than some of the fancier models with fewer heads.
The build-quality seems first-rate, the action that combines oscillation with in-and-out pulsations is very effective, and my teeth are thanking me.