They are better than a manual toothbrush because they have a timer installed in them. The average brushing  time with a manual toothbrush is 30 seconds. When you use the electric toothbrush you brush for 2 minutes. It does the motion for you. You simply guide the toothbrush along your teeth. When you make the first pass and it is still on, you go over your teeth again, again, until it turns off. Hopefully at the end, you remember all the areas your hygienist told you to brush longer or areas you were missing.