I have, and have had for many years, modulators on all my bikes. I've run thousands of miles of experiments and am convinced that they can be quite effective as cage repellents. IF USED CORRECTLY. It's a tool. Like your sidearm, it doesn't put a protective shield around you. It offers protection only if you develop the requisite skills, maintain a high order of situational awareness, and are prepared to use it when needed.
What I've discovered is: Riding with the modulator on at all times is a waste of time. And may well result in the guy riding in front of you dismounting at the first stop and smacking you in the mouth for giving him vertigo. On the other hand; If there's a creeper (one of those half wits who can't decide if he's stopping or going) at right angles to you at the intersection or coming at you in the left turn lane, if you wait until you're 50-100 yards out and hit him with the modulator it will, nine times out of ten, freeze him in his tracks. Same thing with the dimwit drifting into your lane. You position your self right in his mirrors and hit the modulator. In the great majority of cases this will pop him right to the other side of his lane.
In short, the modulator is used to suddenly introduce visual disruption in the cager's filed of view. Left on all the time, it merely fades into the rest of the optical noise out there.