Review (1/5): Don't stand it on end
After owning this toothbrush for a while, I found (as others did), that it drains its batteries in a matter of days. Improving the seal at the bottom with silicone grease didn't fix the problem, so I took it apart to see what had happened.
The answer seems to be that water had leaked into the main compartment from above, causing corrosion and (presumably) closing a circuit even when the brush was switched off.
This is likely due to my having stood the thing on end, rather than laying it flat. There's a (leaky) seam that goes around the entire body, and that includes right under the head. Seems like they could have made a much better design with a single solid piece of plastic, with penetrations only for the switch and the batteries.
I still use it, but I have to remove the batteries when I'm done.