One of these months I'll post a reason to keep your Rugers. The Ruger and Freedom Arms revolvers complimeny one another. That said, a handgun is personal. When it does not feel personal, what is that person doing with it?
As for shooting .38's in .357 chambers, or .44 Specials in .44 mag chambers, interchangeability has worked perfectly out of the same cylinder with S&W and Ruger revolvers for years.
Ostensibly, Freedom Arms cautions against shooting the shorter cartridge in the longer chamber on the grounds of a potential to raise pressure when the longer round is pressed into a chamber fowled by the shorter cartridge. FA chambers tend to SAAMI minimum, whereas S&W and Ruger are more generous. I believe another gremlin may be at work: the risk of not seating a cartridge properly in the chamber, which could bind the cylinder. That and the possibility of a handloader NEGLIGENTLY attempting to force high primer ammunition into the cylinder, may present a hazard.
If erosion were a problem shooting .38's in a .357 mag chamber, I should have ruined a few S&W cylinders. (The same may not be true of firing beau coups thousands of .22 Shorts in a .22 Long Rifle chamber, as many .22 barrels are, or were, of softer steel than centerfire barrels.)
When you order a FA .454 Casull, by all means order a .45 ACP cylinder at the time of purchase, And a .45 Colt cylinder as well, unless you learn to load light with .454 brass. I speak personally, as enjoy hugely the .45 Colt and .45 ACP cylinder in my FA .454 Casull.
David Bradshaw