we have yet to actually see EEstor's caps however we have seen Maxwell's and they seem to be the real deal. They are readily available... albeit expensive. They leak only about 1-5% every 72 hours... though I would be happy with 1% leakage per hour. The Caps main role in our thinking is to act as a buffer to a battery pack, at least at first.
Here is a link to a very capable supercapacitor.