I used to see a guy from a local IRS office with a revolver in his duty belt (maybe two/three years back)... have seen someone recently in the same uniform with a semi-auto. Just didn’t see the guy enough to tell if it was the same guy or someone else. But did notice it, as it isn’t common.
Agencies that used to issue revolvers, and some officers kept them through the transition (NYPD, for example), have got to the point that people who were still carrying them are retired. It is a semi-auto world, now.
As a backup... no problem with my 9mm 642-1. But primary, I wouldn’t want a 686. Maybe a 629, but that would get old to carry fast. Just rather have the extra firepower, considering what criminals can have today. A 686 verses an AK... even a semi-auto rifle... isn’t a fun day. Kind of like that TV movie of the North Hollywood shootout, where they had an actor playing the one officer say, “these guys were slinging AK's and I was carrying a 9mm Beretta. I was in the wrong place with the wrong gun.”