I got my twin-cylinder Single Six in 1971, right after I got discharged from the Army. It sits in a drawer next to the box Ruger sent me to "update" the action from the 5-click to the 3-click version free of charge. But like TMHunt says, there's really something about that cacophony of clicks when you bring back the hammer that harkens back to the Old West, and I'm not sure I want to see that go away, even if it's for free.
When my wife got (briefly) into Cowboy Action shooting, I picked her up a matching pair of Single Sixes with birdshead grips in .32 H&R Mag. Prior to shopping for those, I never knew they were available in anything other than .22. It's a real centerfire example considered by most to be a real self-defense round, but the gun is still LOTS smaller and lighter than even the .38/.357 Ruger Vaquero. Not as cheap to shoot as a .22, but that's why you reload!
I see examples of the twin-cylinder SS in the used display cases of almost every gunshop I go into. Folks are quick to use them to trade up to something bigger when the time comes. Really cheap way to get into shooting handguns.