Some people are especially sensitive to lights, including flashing lights, and lights which point directly into their eyes. Both these two situations can result in migraines for the unfortunate observer.I am glad to read that German law mandates downward-focussed lights. We should do the same.
Flashing lights used to be illegal (i.e. when incandescant lights were the norm) but the law was changed to specifically allow them. However, for the reason above, and also because judging the speed (and to some extent the position) of a bicycle is impossible when the light is flashing could actually make flashing lights less safe. Batteries have improved and LEDs are more efficient, and the battery life even on 'steady' mode is way more than in the 'days of yore' hat some of us knew.