I have two for the 58, for a while I thought I might get into CAS shooting but decided it would be too much work. I can swap the cylinders in and out with no problems regarding timing or lock up. This is a Pietta, no drag marks on the cylinder (that's caused by the cylinder bolt being too high, it can be polished down to prevent drag marks).
For what it's worth, I also have two Pietta 60s: four cylinders, two 8-inch barrels and one 4-5/8 barrel. I have swapped them all around from frame to frame, shot them with no problem, no cylinder drag marks, nada. Good timing and lock up regardless of how I mix and match barrels and cylinders. That says a lot for Pietta's quality control.
If I had to do it over again, I probably would not worry about extra cylinders for the kind of casual shooting I do. However, now that the money's spent, I'm glad I've got them.