Wow, that's an expensive solution compared to buying more than one of the new COB USB rechargeable tail lights. Didn't find any listings for the USB-Werk on Amazon but a couple of overseas sellers show up on eBay with the cheapest being $135 with shipping Busch + Müller USB-Werk für Nabendynamo | eBay

I recently bought four USB rechargeable COB lights - 100 lumens, 500 mAh internal battery and made by the company that makes some lights for Blitzu. Cost was $16 for all four. It's easy to carry a spare if you are worried about exceeding the run time of the light.