The problem with most dyno's is that they take away from your pedaling to light the thing up, and often aren't very efficient in doing this. In other words, you can feel the difference, at which point you wish you never had a dyno in the first place. Sure you can get a better dyno, but it costs more, and at that point, you could've gotten a much brighter and nicer flashlight that runs on 18650 li-pos which last practically forever. You can get great deals on Ultrafire flashlights like these online, btw.