I think that's the main thing - the amount of energy lost by bringing a bike to a stop is nothing compared to that of bringing a car to a stop from 60 MPH.
And they're probably better off just adding a generator in-line with the pedals (in fact, I'm surprised these things have "direct drive" at all and aren't just a generator on the pedals with a wire to a motor on the front/rear hub).
And they're probably better off just adding a generator in-line with the pedals (in fact, I'm surprised these things have "direct drive" at all and aren't just a generator on the pedals with a wire to a motor on the front/rear hub).