Originally Posted by wphamilton

Because a bottle generator will have bearing friction, the magnets or coil spinning on an axis. It will also have some loss in the rolling surface interfacing with the tire. In this kickstarter generator it's the magnetic eddies that are moving, the flux lines cutting across fixed coils, so there is no mechanical friction. When I visualize this, all of the drag is directly related to the power generated, so I expect it to be more efficient in that sense than bottle generators. A hub generator, maybe not much difference but depending on the engineering.

We already know that the drag is greater than the ultimate power consumed by the light and we've got some pretty good data, here and there, on drag from various dynamos so that side doesn't really need any proving. The actual drag from this tech, yes I agree that we need some measurements to put the question to rest. That may be a little tricky for DIY tests though, since a coast-down doesn't get precise enough for that small amount of rolling drag and simply spinning the wheel unloaded doesn't actually translate to the drag on a loaded wheel. So we may have to wait for someone with more sophisticated equipment and a little time on their hands.