How long and how difficult is it to change calibers on either?
For the 550 (and everything else, but I can only describe the 550) it varies a lot depending on what caliber you are switching to.
You COULD need to change 3 elements-
1. The toolhead and dies
2. The priming system
3. The shell plate
My easiest change is 45ACP to .308. I have a toolhead set up with my ACP dies and and powder measure. I have a separate toolhead set up with my .308 dies and a powder measure. 45ACP and .308 happen to both use large primers and the same shell plate. To switch from 45ACP to .308, I remove my 45 toolhead (2 pins and it slides out, and put in my 308 toolhead. Then I have to verify my powder measure is right (it always is) and that my setup is right (it should be). The end, takes MAYBE 5 minutes.
Now to go from 45ACP to .223, I need to change the toolhead, shellplate and primer system. Talking 15, 20 minutes. If you didn't have a toolhead set up for .223 that would be longer since you'd have to adjust your powder measure, OAL, crimp etc.
The lazy but wealthy man's setup is to have a large primer press and a small primer press and a toolhead and powder measure setup for every caliber you load. This is big $$.
The minimum setup is one press, dies and shellplate for every caliber, one toolhead, one powder measure.
Most people fall in between the lazy and minimum. A toolhead is less than $20 so it's worth it to have one for things you load frequently, and one empty one for extra for stuff you rarely load. This keeps your OAL, crimp etc consistent.
An extra powder measure saves some time but cost $70-$80, so having one for a caliber you load for rarely is kind of silly.
I am still pretty much a beginner reloader. I used a Lee turret for awhile and it was well worth what I paid for it for the ammo I loaded and what I learned. I am really happy with the 550 now though.