For flat surfaces, this Porter Cable-7346 dual action grinder is the best tool that I have ever worked with. It’s kind of half way between a big angle head grinder and an orbital. The angle head grinder can get huge amounts of work done, but a moments inattention can do a lot of damage. An orbital takes forever to get anything done. This unit can remove a lot of material but is easy to control. And being electric, you don’t have to wait for the compressor to catch up.