That thing will never touch my car. Too many times while hand claying, I've seen something on the paint that really shouldn't be picked up in the clay. With that thing, you're gonna eventually get to going real fast and before you know it, you'll have some circular swirls or scratches in your paint.
I guess if you took it nice and easy, you could use it. But hell, if you're going that slow, may as well use your hands and do the job right.