M105 by hand is astounding, as the OP clearly proved. I use it by hand on faded windshield trim pieces and on the paint where I can't fit the DA or rotary. It's simply amazing technology.
It doesn't take that much effort to use by hand...it's just that good.
If you like M105 you'll LOVE D151 - same technology with less cut and leaves a waxed finish. By far the best single stepper I've tried.