Yeah, what Ed said: do you want to see or be seen? I also use the Flea for city riding. If I was riding on dark roads in the country I'd want something brighter, but as a strobe which says "there's a bike here!" I think they're good.
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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