The only thing about on your left is people need to say it from farther back. when riding on my daily commute people will say it to me and they'll wait until they are right next to me already, it sounds like someone's mouth is right next to my ear saying "on your left!" and startles the heck out of me. When they say it farther back, I can move right a little to give them room (this is on a street with bike lanes). But when they're already to my left there's little point in saying it.

Even when RUNNING on MUPs I've run right into the casual peds, people don't even look before suddenly turning left.