This narrow brush head is perfect for my son's teeth (just turned 4). The narrow shape allows me to reach all his teeth easily, especially the back molars, which the dentist said needed some extra attention. So that's ideal. The rounded head of the brush also helps with this. The only downside is that, as far as I can tell, there are no bristles on the brush to indicate when the brush needs replacing.
Unfortunately, I can't comment much on the vibration of the head, as my son finds it frightening. Hopefully, we can start using it soon.
The protective cap that comes with the brush is handy so we can easily take it with us when he goes to stay with grandma and grandpa. This keeps the bristles clean and prevents dirt from getting on them (although I do put it in a bag because the cap doesn't seal completely).