If that's a 360 degree swivel mount it would make a good deterrent to tailgaters, but I would mount it on the non-throttle side so I could accelerate away.
Back in the day when tubular sissybars were the rage, I thought it would be cool to replace the horizontal rear-facing tubes with shotgun barrels -- one loaded with birdshot and the other with a slug (for tailgaters who didn't get the message from the first one). I used to keep a handful of BBs in my pocket; a few of those on a following windshield seemed to work. Nowadays, that would get ME shot for sure.