I've been using the sander on a range of surfaces and it's mostly performed well. The speed regulation is more of a gimmick, since the suction is only effective at the maximum speed. My only criticism would be that the machine "leaks" at the seams between the length modules, so instead of conveying all the dust to the bag, some of it is being blown into the room. Maybe it's only my device, but I have been unable to fix it.