When I go into a party store, gas station or any place I turn my back on - I try to use glass reflections, mirror, chrome items to help me see my 6:00 position. It is good to know what and whom is doing what. It also lets you check out the hot lady at the counter and not get busted being a typical male....
I don't do any shooting drills with a mirror...... (yet) maybe someday I will give it a try?