Thom28-
Most who post here use the Hornady die set. The Hornady set generally does a fine job once you become aware of certain peculiarities of using them. These peculiarities are unique to the 450B die set. (Hornady has recently been furnishing seater dies with an incorrect length of die body. See pertinent recent threads about this problem.)
The FL sizing die works as advertised.
The expander/case mouth flaring die is needed only occasionally, for example when loading cast bullets, or when dealing with cases having flawed mouths.
The seater die can be a problem for the uninformed or unwary. Unfortunately, Hornady supplies a generic set of instructions with the die set, describing how to set the die to apply a roll crimp when searing the bullet, and also how to seat a bullet without applying a crimp. Do NOT set the die to apply a roll crimp. The 450B headspaces on the case mouth, and a roll crimp can interferes with proper headspace. A roll crimp may allow the case to enter too far into the chamber, which can lead to various problems including unexpected KA-BOOMS.
(The same seater die is furnished with the 460 S&W reloading die set. That cartridge can profit from applying a roll crimp. Hornady is apparently too cheap to supply a sleeve without the internal roll-crimping ridge for the 450B die, with suitable instructions.)
The fourth die in the Hornady set is a taper crimp die. Unfortunately, Hornady failed to include anything in their instruction set about setting up and using the taper crimp die. Approach its use gently, increasing the entry of the bullet into the die in small increments. Too little crimp doesn't get the necessary job done, while too much can distort the bullet needlessly, and also permit the cartridge to enter too deeply into the chamber.
In short, don't apply a crimp with the seating die. Apply a crimp with the taper-crimp die. You do not require another crimp die.
(Some combinations of bullets and powders do require more retention of the bullet in the case than that produced by the taper crimp die. Certainly this is not needed with the Hornady 250-grain FTX bullet. It may be useful with a light bullet. When and if you encounter such a case, then it may be time to consider obtaining a side crimping die. Most such dies are made by their owners by modifying a Lee 45-70 Factory Crimp Die. See the sticky threads in this section about such dies.)
CH4D produces well-manufactured dies:
https://www.ch4d.com/Other posters will be along soon to correct or elaborate on my comments. Good luck.
--Bob