Too bad, often blows!

As such, a great device. The disadvantages described by others I do not find that bad. In order that the device is not waterproof, you can live. A few drops of rain holds off the unit and in heavy rain you can pack it in a bag.
Because the device works so well, I have more bought later after the first purchase 2 for my sons. Of these 3 devices are now 2 blown. As soon as one a little too fast shuts down the mountain, the voltage (hub dynamo) is too high. Then the device is unusable. The mobile phone has this thankfully gotten nothing.
My recommendation for those who have already purchased the device if connect as described in the instructions, but parallel to the light. And then always drive with your lights, especially downhill. Thus, the voltage (hopefully) is not too high. But then the power when the phone is no longer to load (about 160 mA) ranges.
I would give the unit 5 stars if it would be a better voltage limiter installed!
The charge controller Kemo M-172N KEMO M-172N Bicycle charge controller USB is much better! Kemo has recognized the problem and revised its unit (old version M-172). He can now cope with input voltages up to 70V. Of course I have not tested, but he has so far held and I am very happy with it. Unfortunately, it is significantly larger.