I have been looking at that. I want to figure out how they stacked the two gears on the electric motor. I want to build an electric drive similar to that but with a more conventional bike. I figured out the gear ratios needed, but have not figured out how to make the gears work, it is almost like you need to thread a fixed cog on first and then a freewheel on top of that.
600 watts powered through a cogset would be pretty crazy.