So I fired mine up last night. Pretty darned fun. What's pretty clear right away is you need the accessory pedal... AND it needs it's own power supply (my pedal-train PS won't cut it). But the sound quality is very good, the selection of beats is very cool, the UI isn't bad at all. So far, I dig it.
Just to be clear--- the unit comes with a power supply.
The accessory pedal(s) are switches---- no power needed.