The Porter Cable rubs the polish or whatever your using into the car in a random circular motion. A polisher like the one you are talking about runs only in a round motion, it builds up heat very quickly and can create massive damage as fast as it can repair a massive problem.
Most of us would agree to use the Porter Cable on the everyday car and the Polisher on the touch jobs. If you only have a polisher it's fine, just make sure you operate it with a little extra caution.
