Dynamo is the general term for electric generators from mechanical displacement. I'm not talking about the small contraptions that power lights on a bike, these are traditionally even worse in efficiency.

Lets be charitable and call it 90%, it's still going to charge the battery (which is described as a buffer), and that will have a max of 95%, discharge the battery, same, and power the motor, which has likely the same efficiency. You're at. 9.95.95*.9 = 73% efficiency at motor output. You're giving 27% to the gods of thermodynamics, unless you like the extra complex cardio you're getting, I don't really see the point. Regular bike transmissions are not free either, but they're closer to 95%.

Thinking about all that, I don't get why they didn't use a hub motor. Why adding a belt when you could have transmitted the power directly to the wheel?