Jim uses two mirrors while riding in greater Boston.
I use one mirror, either on my glasses or my helmet when on a bike, three mirrors when I drive a car, and no mirrors when I walk.
I won't put words in Jim's mouth, but to me mirrors are useful, not magical. They are a huge help with situational awareness. My inner voice sometimes sounds like a NASCAR spotter.
But I NEVER direct ("acknowledge") traffic while driving a car or riding a bicycle. I drive my car, they drive their car. I ride my bike, they drive their car.
I don't direct ("acknowledge") traffic while walking either. I walk my walk, they drive their car.
P.S. There are M*******s who are hostile the moment they open their car door and get in. NOTHING we do can change that fact. NOTHING.
-mr. bill