I've been using an Oral-B rechargeable toothbrush for over a decade, I still have the same one with the same battery in it, a testament to Braun and German engineering.
I wouldn't be without it. I have used it whilst away at 3/4day Conferences without the charger and although there was a noticeable drop in speed/power it kept on going.
I have found the best place for replacement brush heads is Amazon, the quantity and prices are very good, with good delivery times.
I find the Heads which have a colour coding in some of the bristles, last a reasonable length of time. And it is easy to identify when the brush head needs replacing.
My only gripe is that, unlike a manual toothbrush, you don't have the choice of "hardness", perhaps this dates me :-)
It is waterproof and reliable and the heads are easily changed. Another plus point is the use of different coloured rings that can be attached to the base of the brush head, so that individuals can have their own brush, a simple idea but an effective one.
I believe that an electronic toothbrush is more effective than a manual, in as much as you can get into the little nooks and crannies more effectively and efficiently.