This is an interesting topic. In my riding club there are a couple who have their bikes equipped with the modulators. I noticed them right away so they clearly draw the eye.
But as mentioned above, I have also had them behind me and I find that they draw my eye. Which means if they are behind me they are a distraction. In cases of a tight formation if I go down (due to being distracted) they will go down too... on top of me.
So I personally have mixed feelings about them. I don't know the specific laws but my understanding is they cannot be used after dark.