I was thinking of exactly the same thing but we don't have those here in Japan that I can find yet.I am also among others who like the Zefal Spy mirror for its compact shape and ease of adjustment, but was disappointed with the optical quality of the mirror itself. I found a really easy hack to upgrade to glass mirrors for about 6$ at a local auto parts store. These are small irregular oval shaped convex mirrors intended to be glued to the surface of automotive mirrors. They happen to fit only slightly larger than the Spy mirror, and I’m very satisfied with the image.
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I can't find any shape other than circular in my local auto parts stores. I ended up getting a rectangular shape mirror 4 for $11 from Amazon. Just tried it yesterday. It improved the image quality by light years! Thank you for the hack!https://www.autozone.com/safety-and...r/p/pilot-oblong-blind-spot-mirror/630945_0_0
These are the ones I used to stick to my Zefal Spy mirrors