Yes, Zoran, absolutely agree. Exposition time is very important. I was doing my hood a few days ago with small, 13.5 cm pads (Scholl Concepts & Menzerna) and it lasted forever compared to my 17.5 cm pads (Riwax). And my hands were tingly after the session - and that's with a rotary, where sightly off-center pads can cause the same problem.
Lauren, are you listening? Remember when I told you about dangerous frequencies? I hope your son will try a Festool or something with very little vibration, so his problems won't manifest again...