Tried using a flashing headlight once, but found that you couldn't even see it because my main headlight overwhelmed it.

basically, the 'to see' light is so bright that it overwhelms any flashing 'to be seen' light, making them redundant. if i were to find a flasher powerful enough to compete with my steady light, id probably just set it to steady as well to get even more ability to see the road....
conclude, no point in flashing except as either a stopgap where you don't have a 'to see' light available or where street lighting is already good