What I'm not clear here is whether this does regenerative braking, or only charges at home. If it's regenerative, it's awesome and I want it. I've actually wanted to do a DIY regenerative braking project for a bike for a long time (impracticality and net-loss-due-to-added-weight would not really bother me as long as it worked). Somehow, if it's only charged at home, I feel like it's kind of silly, like a way to make biking lazier.

Still, in any case it would be awesome in that it would make biking practical in hilly areas where it is otherwise a horrible mode of transportation.