Multiple things going on here, and in every case, it's operator preference rules.
I have both Security Sixes and Speed Sixes. For me, I prefer the round butt for shootability as well as carryability. And the adjustable sights of the Security Six never get in the way or snag. Therefore, my favorite is a round-butt Security Six. They were not catalogued, but for a couple different reasons, there are some around.
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