A double-action service pistol does make a decent back-up weapon, when carrying a good sixgun.
Actually, I am more-or-less paraphrasing the late, great sixgunner Elmer Keith, who was referencing the S&W Model 59, and perhaps the Model 39, when he was writing about this, if I recall correctly.
I am certainly no Elmer Keith, but have commented multiple times that a compact Glock is a good "tactical reload" when carrying a revolver.
In the 2002-2004 time frame, I actually tended to carry a G29 and SP101, together, during personal time, and it was not clear which was the "back-up."
I remember Tom Givens' mini-class at the Snubby Summit, in which he certainly did make a good case for the Kahr PM9 as the better choice, than the small-frame snub-gun, for a back-up weapon. I had, before that time, already tried a Kahr K9, to see if it could displace the SP101 as my favored compact handgun. The K9 had gone away, and another SP101 soon joined the first one.
I will admit to having been neglecting my revolvers, lately, while concentrating upon building my skill with G19 pistols. My revolvers have been relegated to house-gun use, as I have not yet renewed my qual with any of my revolvers since they lapsed last October. (PD rules apply 24/7/365.) I do plan to remedy that, soon.
To be clear, I am not biased against auto-pistols. My first handgun, in late 1982 or 1983, was a 1911, and at the time, I thought revolvers were quaint relics. I had to use revolvers, however, 24/7/365, during my rookie year as a police officer, 1984-1985, so made a diligent effort to learn the weapon system I had to carry during what was Houston's violent boom-town era, competing with Detroit for murder capital of the USA. I learned to love both revolvers and autos.
Officers Debbie Lokey and Phil Bankston guided me through the process of learning DA sixgunning, in the Houston PD academy. (Debbie Lokey used to teach privately, too, but have not heard that she still does so.) I also diligently read the words of the late Bill Jordan, the late Jim Cirillo, and Mas Ayoob.
The only private revolver-specific live-fire instruction I have attended was Michael de Bethencourt's mini-class at the Snubby Summit. I do highly recommend him.