Review (2/5): After 4 months No Longer Works
At first I thought this was going to be the solution to the problem of the original rechargeable Sonicare toothbrush with batteries that can't be replaced (my original Sonicare stopped holding a charge).
However, after only four months (just long enough to waste money replacing the brush head!), the button began to only work erratically, and now it does not work at all (can't power the toothbrush on).
The reviews that state that the battery compartment does not keep water out are completely true. The battery compartment is always moist, and the batteries will begin to rust.
I was pleased that my Eneloop batteries worked well to power the toothbrush, so I could be using rechargeable batteries, however it doesn't matter if the toothbrush itself doesn't last past 6 months.
The batteries that came with the toothbrush lasted around a month. The Eneloops needed charged only once in the next three months.
Looks like the Sonicare brand just fails on too many levels, regardless of whether you are using the ultra-expensive rechargeable unit, or this unit with two AA batteries.
[Update] Flashlights have had "screw on" caps for nearly one hundred hears. The Sonicare toothbrush is the same form factor. I have no idea why someone at Philips thought a "clip on" cap (vs. a screw on) would be better, ESPECIALLY for something you use with water. I am still COMPLETELY BAFFLED by why they would use this design. The battery compartment will ALWAYS be moist. Being able to use rechargeable batteries is clearly superior to being stuck with the Philips Soincare charging station. However, the fact that your batteries get wet means you will eventually ruin your batteries. That said, I am about to purchase another one. Being able to use your own batteries makes it a when, both for the fact that you can replace the batteries and also so that the (much more expensive) toothbrush isn't useless when the internal batteries fail after a year or so. Unfortunately there is no better alternative at this pricep oint.