Just nudging this thread forward to the present to let everyone know that they now have additional models. As I understand it, the original one just flashed when the magnets passed by. They now have models with capacitors that get charged and in turn power the light. That allows the blinking speed to be steady (although not adjustable), and to continue for a few minutes after stopping. It also allows for another model that has a steady light.

I got a set of these for Christmas (from my LBS), and I'm pleased so far. Granted it's maybe too soon to see about the spoke problem, and maybe there is a little bit of drag. But I do like the simplicity of no batteries, even if you would only need to change them once a year or so. I probably like them for the idea as much as for any practical reason. Batteries can be toxic to manufacture and discard. Granted, so are electronic circuits.

As for visibility, I agree it's definitely a "to be seen" light, not a "see with" light. I think the taillight is not any dimmer a cheap blinkie. I also agree that neither the front nor the back should be your only light, but I think of it the ultimate dependable backup.