FWIW, I have both the new and old models of the Luxos U. The new model doesn't have much mileage but the old model has performed flawlessly for me, including for 8-hour stints in heavy rain while charging my Garmin Edge, even though it's not officially recommended. The plug connecting to the lamp has to be pointing down.
UPDATE: After many thousands of kilometres, including a good deal of rainy ones, my original Luxos U has failed after a long day in the rain, just 2 weeks after my last post. It started flashing and couldn't be stopped, whether I was riding or not.