I'm usually wary of 2-or-more-in-1 inventions; more often than not, they end up doing neither thing very well. Like sporks, which are barely suitable for eating KFC "mashed potatoes", but nothing else.
But this teething ring/toothbrush seems interesting, and a lot less threatening than giving a baby a long, pointy, toothbrush-shaped implement. I wonder if they couldn't have even more brush on there, though. I swear, given her toddlery incomplete technique, I'd guess at least 75% of the kid's actual teethcleaning comes from gnawing on the nailbrush in the bathtub.