I have a 15" convex and prefer convex to flat for the wide-angle view. There are a lot of options at about $20.
Something to note is that the 1.75" clamps that came with my mirror wouldn't fit between the ROPS bar and windshield.
I bought a different strap-type 1.75" clamp that would fit under the windshield (and used the mirror clamps for a shovel mount).
I agree with others that the rearview mirrors tend to be pretty high up out of your sight line. The benefit of the other clamps is that they are longer and dropped my mirror lower. If it's a big issue, I'm sure a little handy work can extend them more.
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