I broke a mirror recently, which caused me to try out several I've had around. One observation that struck me is how much better a mirror with a good optical surface is than a mediocre one. I think many bike mirrors that use metalized plastic (cheaper, less likely to shatter) are optically mediocre. The Busch & Muller Cycle Star (4 models available) stood out for optical quality (vs some Zefals and a Cateye model); it is just slightly convex and provides a sharp image.

Also tried eyeglass mounted mirror again, once again without adjusting to it (right eye dominance does not help here). I have some front-surfaced mirror material I may try as the double-image ghost from the usual rear-surfaced mirror is a problem for me for some reason.