They do a good job in cleaning your teeth and breaking down plaque and also massage your gums and are better in preventing any periodontal diseases.
Hope this helps
Most studies show that most powered tooth brushes are not more effective then a manual tooth brush. That being said, the only one that was more effective is one that rotates/oscillates. I believe the spin brush fits this description. However, the difference in effectiveness was also shown to be insignificant.
Good luck with your tooth brush shopping!