I have had a lot of expensive and time consuming dental work done over the last five years, so I am a really motivated electric tooth brush user. I have used at least three different electric tooth brushes and the Colgate 360 is by far the best, while also being the least expensive.
It is powered by one AAA battery so the handle is slim and easy to pack. The one battery lasts a long time. The brush has a non slip rubber on/off switch that has a satisfying click and is more intuitive to use than the two battery brushes with bigger handles. There is no worry with expensive replacement heads. Just buy a new 360. It also has a tongue cleaner feature that I haven’t seen elswhere.
As an aside I took one of the Colgate 360 electric tooth brushes apart to see what makes it work. It has some really sophisticated engineering. The on/off swith is a formed piece of metal that clicks open and closed like the clamp that women use to hold their hair curls at night. The power source is a vibrator in a metal cylinder and the energy is transmitted to the brush head by a rigid plastic rod encased in a flexible plastic sheath. Cool stuff.
[Note: Instead of throwing these away when the bristles get soft, put them to work cleaning in the bathroom or kitchen, or on small parts in the shop. The electric models are especially effective for these tasks.--OH]