When I was a kid, I had a bike with a generator lighting system where the generator rolled on the side of the tire. When I used the generator I felt like I was going nowhere fast and I only used the generator when going down hill and when I had to have a light. I am guessing that the generator was probably about a 3 to 5 watt drag on my engine. So this should compair with the loses in the hub. If you put a generator light system on your bike and ride you should be able to decide if the hub is right for you.