When I looked at your link I immediately said, "Whoa! That's a little too much". Something that is just a box of silicon chips shouldn't cost so much. This one here is a more realistic price and throws in a cheap dynamo and cell phone mount to boot. Not that you'll need those since you'll probably get a nicer dynamo hub ( I'm guessing ).

It would also be nice to know what maximum current output is possible with the charger that you buy. None of the ads mention this. It would also be nice to know if it works with an AC and/or DC input. Most dynamo's I believe output AC. A few DC. If you have a dynamo that outputs DC you might have a problem. Once again the ads don't mention input requirements, I have to hate when technical info is left out in ads.