The small ones are very powerful and work harder to deliver the power. You are only supposed to use them for about 10-15 minutes at a time. If used over the recommended time, it will overheat and cause damage to the motor. After too many times, it will die. I have gone through three wands and expect to buy many more. They are super powerful like the big ones, but are easier to use, lighter and do not make me numb.