I'm not rating this specific pad but the whole system. I just didn't see anywhere else to rate it. Anyway, I purchased the adapter for the 3401 and used these pads. Be WARNED if you place to much pressure on the pad trying to remove defects or if you use it near a curved surface with even minimal pressure the nylon portion of the plate inside each pad can rub up against the paint and leave some melted plastic there that then has to be buffed off to remove.
I worked around this for some time since I had t but with the Flex finally releasing smaller backing plates people need not suffer that abuse any longer.