I've used my strong dry 15 inch machine maybe 5 times or less...I even got the black brushes from strong.
Bought it on ebay, but I still don't think they're worth the $ (new), $1k tops, and we barely use ours.
We use the 360i as the primary tool (soon zipper), so the crb doesn't get used that much, prevaccing w/ it works great, but we feel w/ the resonators just takes a lot of time, stopping, etc.
I'm not "sure" either...but if I had to guess I think I would be right................and given the fact that the number sold based on their feedback exceeds the number the had "left over" according to the "story" in the listing I'd also guess that this is just a way to sell around their distributors..