I have a real hard time believing that an "off-center" bullet (ie the case mouth expanded more on one side than the other) could possibly damage a revolver, if the load is not excessive and it chambers OK. After all, the cartridge is presumably laying in the bottom of the chamber when the primer is hit with the firing pin! It is never perfectly centered, there has to be some tolerance (or case has been neck-sized for a tight fit in the chamber, etc.). I do use a RCBS case master with my rifle rounds, but not for handgun. On handguns I like the "M" dies for expansion as this does seem to help center bullets in the case, but more of a matter of 'looks' and convenience when reloading, rather than results, at least for me with open-sighted revolvers. Some might be able to tell the difference with perfectly concentric handgun ammo, but I can't.
On the subject of .45 Colt vs. .454 dies, I can see both sides. Lots of people don't have problems using .45 Colt dies for .454 Casull. But FA doesn't want to have to take phone calls from those who do have problems. So FA recommends certain dies only, even though others may work.
Now Dillon, on the other hand, doesn't want people complaining that the press is difficult to use for a certain caliber. So Dillon makes the dies with a larger opening so alignment is less critical (says so right in their publications). So in a sense that's really an opposite approach/reaction from FA.
Taz, good luck with your .454. I'm sure it will all work out.