I find the disposable ones are overall cheaper and the batteries last about as long as the brushes. Unless you are inclined to replace your head often as such people may be than they might be a better option.

They are more like vibrating brushes and reality is quite simple in design. Less complex then the replaceable heads that have moving parts and seals etc. After using both, I find that work just as good and both are noticeably better than non electric brushes.