I guess I'm going to be the main guy playing devil's advocate and sticking up for these things.
For each of you complaining about how annoying they are, you pretty much proved how effective they are. Any time I come upon a bike with these installed, they IMMEDIATELY catch my eye, which is exactly what they are supposed to do. If I annoy you but you see me and don't endanger me, I think that's a pretty good tradeoff. By the way, if anyone complains about how annoying these are but has loud pipes on their bikes for "safety" reasons - well, the term "two faced" comes to mind.
The website I bought mine off of recommends having this feature active on high beam only. If you're riding in a group of bikes or caught in a line of slow moving traffic, you can switch to low beam and disable the modulating. Yes, there is a photocell that lets you use low/high beam in a normal fashion after sunset.
Someone said they'd never install this because it could fail and leave you driving blind at night. Light bulbs never fail? Fuses never fail? You ride within your limitations (slow down at night), pull over, and deal with whatever broke, just like any other malfunction.
Let me add that everything I've said so far is based on website info, instructions, and my own brain cells. I have not installed this yet. When I do, if anything causes me to change my tune. I will come back and rebut myself.
Sorry for the long post but I couldn't believe how many guys jumped all over this in a negative way when I feel like it's a valid safety enhancing device.