Despite being more than little bit similarity to the Griffin PowerMate knob (I have one sitting on my desk), the allTunes MP3 knob is made for MP3 playback, unlike the PowerMate's general purpose volume adjusting. Press down to play/pause, twist the outer knob for track forward/back and twist the inner knob for volume adjustment.
We think the knob uses USB, but there's nothing in the press materials that says anything about how it connects. Nor are there any release dates or pricing info. If you are looking for a knob to use for your computer, the Griffin Powermate is pretty fun.
PowerMate Product Page [Griffin]