I don't think I qualify for this discussion.
I dive mismatched fins. They're fine, whichever one I put on whichever foot.
About 7 years ago, I was helping on a "drilling trip" at Stetson Bank, on the SPREE (Frank's/Wookie's boat), where you drill (big pneumatic drill) to make holes in the reef substrate for new mooring anchors to be cemented into). You have to be fins-off since you're standing on the bottom. So you put your fins somewhere where they will stay put.
But one of mine didn't--and drifted off who knows where, probably off the bank and into the deeper water (these were the boxy square fins that were popular 20 years ago). Frank--always the gentleman--gave me an orphan fin from the boat's supply of same. It's silver and longer and more slender than my faded-green box fin.
I guess I'm not that particular. And I'm easy for my buddy to spot.