I've used the Dremels and the Black & Deckers, imho the B&D is a far superior machine. The brushes seem to last forever, the grip is more comfortable, it has less vibration, and it is flat out more powerful.
The digital read out is a uesless gimmick, unless your deaf and can't hear the pitch escalate along with the rpm, but even then I guess you could tell the speed from the torque.
Either one is a very handy tool. But the B&D is the better choice.