I also have the signal dynamics brake light modulator, I chose it over the www.kisantech.com modulator because like birdie_xx said it repeats itself the kisan doesn't.
BTW if you install one make sure you wire it in right at the tail light, the first time I installed mine I figured I'd wire it into the loom near the battery but then it only worked when one of the brake levers was engaged.
I also use there headlight modulator, it really makes a difference, I can see people looking at my bike trying to figure why the head light is flickering I even had this guy pull up next to me to tell me there was something wrong with my head light.
Plus it has a feature that at night(there is a photo cell that doesn't allow it to work at night)if you blow the horn your head light will modulate(slowly) for 2.5 seconds.