Had you only said for BUG use, I would have said the J-frame would be fine. But since you also said it might be for times when you need something smaller as an ONLY gun, I hesitate to do so.
They are just so hard to shoot well.
And by "well", I don't mean standing and trying real hard to shoot your best group with. I've shot some pretty groups with them when trying hard, but that's different than your intended use. I mean putting rounds into a small area, as fast as you can, while shooting a gun with small sights, a tough trigger, that squirms in your hand at every shot. Oh yeah, you, and the target, may be moving, ducking, weaving, etc at the time.
While a J-frame beats everything from having nothing, to a sharp stick, to a .32 auto, I still want something easier to hit with.
While a LOT of people stroll around everyday with just a J-frame and are all happy, I'd really rather carry something easier to shoot.
I've carried several J-frame models over the years, settling on the 442 Airweight Centennial, but have gotten away from them after getting a Kahr 9mm a couple of years ago.
It has better sights, a better trigger, holds a couple more rounds, and mostly- I can shoot it a lot better than any J-frame I've had.
I've always felt OK carrying a J-frame as a BUG, but never felt very good about having ONLY a J-frame. And I think we need to look at it from that point of view- what if it IS the only gun you have, since that's basically how things must be if you need to need to use it.
I would feel a lot better carrying only the Kahr than only a J-frame, and all because of how much better I can shoot the Kahr.
If you get one, practice and train with it. They are the hardest guns to shoot well, but if needed- is the one we need to shoot very well.
Not that the small revolvers are worthless.
Their best feature to me is that they have a better shape for the pocket carry I usually use. The cylinder holds the pocket out a little so I can get my fingers around the grip easily.
The general shape of a Centennial slips out of spaces like pockets easier than a semi-auto too.
I still have my J-frames. I can't give them up that easily.
But I usually only carry one when carrying a third gun (and I usually carry a third gun as an "in case I need to loan my wife a gun" since the revolver is what she likes).
Now, why I like the 442 Airweight Centennial-
Airweight, because I think it's the best weight for me. It feels enough lighter than a steel frame that I can feel the difference in my pocket, but the recoil isn't near as bad as an Airlight or Scandium.
Centennial, because I see little chance of needing a single action shot. Also, on the Centennials, the frame comes up a little higher in the back to spread the recoil a tiny bit better.
If you get one, practice and train with it. They are the hardest guns to shoot well, and are used in the cases we need to shoot best.