There isn't nearly the room you think there is under your front rack. Adjacent to the rack might work but leaves the light either ripe for getting hit or one side of the bike blind. Mounting at the axle leaves the bike susceptible to splashes and throws the light too horizontal. B&M specifically say not to mount the light at the axle. Also they say that a dynamo light mounted mounted upside down won't have good optics & is likely to fill with water. Between the fork crown and the handlebars is best.

I am pleased with the B&M Lumotec IQ-X it's 100 lumens, but has a narrower throw & weaker plastic mount than the Luxos U. I think the driven led's are likely the same but The Luxos U IQ-2 is nominally 70 lumen, largely on account of the wider light distribution, thus lower light "density". The Luxos U IQ-2 will do 100 lumens for short periods of time until the internal cache battery depleats. The Luxos U IQ-2 also has a remote switch I don't like because the housing broke after 50 miles, & the switch seems susceptable to water intrusion & has to be mounted somewhere. So yet another wire.

The problem. with dynamo lights rests purely on the number of electrons you have in supply. Bright & focused or less bright & distributed. Either light I mention is plenty bright enough to ride by, but my preference is the IQ-X due to it's simplicity.