I lived opposite a crack dealership when I was a courier in SF. Our corner liquor store held the record for Most Robbed in North California that year. And your view of crime is, I am afraid, somewhat more reflective of Westerns than real life.

...In Westerns, the bad guy says "Draw, podnuh!"

..In real life, a bike mugger hits you, without warning, with a piece of pipe. Or maybe grabs you at a stop - in which case he'll stand a better chance of getting your *** than you will if you're a woman. You'd be better with a knife, I suppose - but still not exactly "good". Because you'll either be trying to wrestle while on your bike, or having already been grabbed.

The big thing to understand about real criminals is that they don't give warnings. Which makes "a tool to protect yourself in the event of a crime about to happen" not much use. Especially on a bike, where if you do get warning you have to choose between readying a weapon and riding.