Blinking lights are illegal in Germany. However you are expected to have properly mounted reflectors and lights within the minimum and maximum brightness levels, properly aimed.

Think about an intersection with a modest group of cyclists (say 20) all with blinking taillights and crazy rim lights headed in different directions, at different speeds. It'll look like some crazy disco, with all those lights fighting for your attention.

If you're just a lone cyclist on the road, then I can understand. But in larger groups, it's confusing. Never mind being a cyclist behind another with blinking lights on a tour, where you have to stare at that non-stop blinking for hours. It'll drive you nuts.