While I like revolvers and J-frames a bit, I will say this--

It is advantageous, if you're going to carry a BUG, to carry one that's as similar to your primary as possible. If you've limited time, it means you've got one less manual of arms to practice. And it's easier to make the switch under stress from, say, a striker-fired pistol to a striker-fired pistol, instead of from a striker to a SA, or an SA to a DA/SA, etc.

However, switching from a pistol with no manual safety, to a revolver, isn't a terrible switch.

Having the same ammunition for both guns is advantageous as well. If you've got two revolvers, both chambered in .38 Spl, with 5-round strip loaders, you won't have to dig around two different pockets and remember which gun's ammo is where. Or experience the irony of a disabled primary with two full magazines available, and a BUG with no ammunition left.

The slickest setup I ever heard of was a certain well-known police officer who carried two Glocks, a full-size and a compact, in the same chambering, since the compact could utilize the full-size magazines.