I can't stand myself for it, but I want one. I love the idea that I can recapture the energy I've generated by riding up a hill, instead of dissipating it by heating up my rims. It is such an elegant solution, avoiding the dirty necessity of plugging into the carbon-fueled grid which muddies the green of most e-bikes.
Plus, as I read it, you don't have to connect it to an iphone, which I don't ever plan to have, any more than you have to mount any other computer (gps, etc.) to your rig. I keep my bars free of any electronics besides lights, because when I'm riding I find most any information I can't glean by looking ahead to be extraneous.
I would also bet that while the batteries are in the hub, they're not part of the rotating mass--they're more likely fixed to the axle/armature. Even if they are spinning, at least they're close to the center, which minimizes the effect.
This is making me reconsider my mostly negative feelings about e-bikes. This could tip the scales toward riding on those rare ocassions when I choose to drive.