I use a B&M headlight and taillight with a bottle generator. That lets me disengage the generator when I don't need it. Yeah I know, it has mechanical drag that a hub dynamo wouldn't have, but that has never bothered me because I typically use it for less than 20 miles and I could easily run it longer if I don't need to go fast. The beauty of a hub dynamo or generator is that you never have to worry about batteries running down. For example, I can run it while commuting on overcast days and not feel like I'm burning off battery life. It is probably not much heavier, if even as heavy, as good batteries and spares would be.