I disagree about the bottle generator... It has no drag when disengaged, and it only is needed sporadically when touring- only when being caught out at night somewhere, which is an unusual situation. A little sidewall wear is no problem in that case. A generator hub has some extra drag all the time, and will be more reliable. I'd get a generator hub if I were doing lots of overnight rando's or commuting in the dark with an aversion to rechargeable batteries. .