I personally don't have one, but I know a lot of people who swear by headlight modulators. The downside is that, here in Texas at least, police love to pull people over for them, since according to Texas law, they are not legal. I don't know if anyone else has this problem anywhere, but there's a simple solution...
Federal US law states that they are legal.
http://www.webbikeworld.com/Motorcycle-technical-articles/Modulator-regs.htmFederal law also states that the laws of a state cannot over ride that of the nation.
http://www.nhtsa.dot.gov/cars/rules/standards/chapt301.html#30103.
I know several people who carry copies of these laws with them, and have used them as aids to either escape tickets or in court to show that they were, in fact, following the law.
For our Canadian brothers, here's the applicable Canadian law:
http://www.webbikeworld.com/Motorcycle-Safety/Modulator-regs-canada.htmJust thought I'd throw that out there in case someone might be interested or in need of it!