you can't use blinking tail lights in the UK or most of Europe as far as I'm aware. (I know someone will correct me on this)
use both for best effect. one flashing to get attention, and another solid to allow people behind you to get a good judgement on how fast they are gaining on you.
for in-city use, PB super flash is one of the best in this regard.
You in fact are wrong. It's Germany (perhaps there is another country or two also) that has goofy light regulations.