All this talk of 'hearing' your surroundings is moot if you read the volumes of flame in the iPod threads in this forum. I am from the school of turn and look, always be aware, plan ahead, think of contingent scenarios. Sounds like a lot of work, but it is second nature. Not that I don't trust mirrors, but I would turn to look to verify what I saw in the mirror. I do this in my car, you know, blind spots - they truly exist.
Mirrors may help some, and they may even help me. I have considered trying one, but always find other stuff to buy.