Not an upgrade, an addition -- my other good dynamo light is a Philips Saferide, which now lives on my touring bike.

Touring bike has a first-generation Schmidt SON dynohub, commuter has a Sanyo, no noticeable difference in light performance if I swap wheels.

The Luxos U has a wider beam pattern, especially at lower speeds -- its beam pattern changes with speed, accessory flood light LEDs on the sides that come on at lower speeds. I don't have the facilities to do a scientific test, but in use, it feels like the Luxos should be significantly more visible to cross-traffic at intersections, as well as being more visible when stopped.

Luxos U has slightly higher total output, not enough to be worth upgrading from one to the other, but double or better what older LED dynamo headlights put out.

Luxos U has a battery-backed standlight instead of capacitor, so it holds a standlight charge longer (over the weekend or longer) and can also run all output on high-power mode, 90 lux vs. 70 if I remember correctly.

Considering the Luxos U costs less than I'd spend on gas for a month of commuting by car, I can't see any reason not to buy the best dynamo headlight on the market. I think that's the Luxos U at the moment, but the Philips Saferide is still right up there.