I've been using the Luxos U for a while now. The first one I had failed quite quickly - it was the original type with the unpluggable USB lead - Rosebikes replaced it promptly without fuss. The replacement has the cable permanently attached so water ingress at the joint shouldn't be an issue.
However, recently, it has started to behave a bit erratically. The function which causes it to change from near-field illumination to 'up the road', which I understand from the 'Germ-lish' instructions is speed related, seems now to operate at random. I suppose it's a subjective thing but I find that when the eyebrow LEDs (which light up the near-field) go out the effect is to make it seem that the light has dimmed. Consequently, just when I need the light the most, when I speed up (which I grant you, doesn't happen that often!) it goes dim.
I know that there is some kind of option to adjust the speed at which the transition occurs - I haven't tried it yet - but I'm wondering if the Luxos is just a bit too clever. I really appreciate the USB power function, which runs my Garmin ad infinitum but if it wasn't for that, I'd be tempted to revert to my Lumicycle which JUST WORKS and which I carry as backup anyway.