I've been pleased with the Comagination sS115H4 headlight modulator. It's small, very easy to install, and has been extremely reliable. Each of the bikes that I regularly ride has one installed.
Many folks, including several forum members, find headlight modulators to be very irritating and absolutely despise them. This topic is almost as controversial as politics and religion.
There is no doubt in my mind that a rider is much more noticeable with one.
I usually have mine enabled while riding in the congested metro Atlanta area. But once I'm on the open road or riding in a group or in an area that is not congested it's disabled.
It is controlled by the dimmer switch and a photo-detector that senses daylight. With the dimmer switch set to low beam the modulator is disabled. With the dimmer switch set to high beam it is enabled during daylight only. The modulator is always disabled at night - high beam operates normally then.
I have a taillight modulator that flashes five times, then goes solid whenever I touch the brakes but I decided to go a different way on the front. I mounted a LED headlight on either side of the main halogen headlight. The stator doesn't take a hit but I am much more visible than before. And nobody is annoyed.