@ work4bike: the Mirrcycle is mildly convex - images are about half the size of those in a flat mirror, meaning field of view is doubled. That seems like about the right compromise if you have to make one. So the cheap mirror is 6x. Too bad makers don't put the shrinkage factor on the package. Now that I'm tuned in to the variability, I'd take a flat mirror to the bike shop to measure convexity. In the end I'm keeping both on my bike - only way I'll feel definitely aware of what's behind me, without turning around.
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genec: is it the mirror that breaks, or the stalk? My LBS sells replacement mirrors, for 1/4 the price of the whole thing - maybe a lot of people have your experience.