B&M have always quoted Lux. I suspect that's what the German lighting regs use.
Other (non-German) manufacturers tend to stick to Lumens, as that's how the LEDs are specified by their manufacturers and avoids any complicated testing or mathematics to account for the effect of the optics. They're also standard for torch manufacturers, as unlike bike lights, torches aren't normally used at a fixed distance from the subject they're illuminating.
If there's been a shift towards Lux, I suspect that's indicative of B&Ms increasing market share.
(As optics are so important, my preferred units for comparison are power draw / runtime, and subjective illumination when seen in close proximity on night rides. Lumens or Lux, on their own, tell you very little. Photographs taken in controlled conditions are also good, but hard to come by.)
