I have recently started using a take-a-look eyeglass mirror. I ride in NYC and I disagree that it is a distraction. Probably those who think it is a distraction only rode with it once or twice and didn't take the time to get used to it. It's a tool in your safety toolbox--no, it doesn't replace turning your head, but I feel it is beneficial to my awareness. My advice is try it for a week of commuting before you discount it.
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1964 JRJ (Bob Jackson), 1973 Wes Mason, 1974 Raleigh Gran Sport, 1986 Schwinn High Sierra, 2000ish Colian (Colin Laing), 2011 Dick Chafe, 2013 Velo Orange Pass Hunter