Okay, some boni fides: Been reloading for awhile now, started on a single stage/turret press. Bought standard dies for every caliber I loaded for. Wanted to go progressive for my competition handgun ammo, only one caliber, at least that was the original plan.

Ended up buying a Dillon Square Deal B used from a fellow competitor for $150. Bought 2 caliber changes, proprietary or not, and went to work on cranking out good ammo. Thousands of rounds were loaded on that first press. Since then, I bought two more so I didn't have to keep changing the press over. Bought one from another shooter for $150 and one from ebay for $200. I got a bunch of extra stuff in those deals too.
I gave one to our oldest son, with 45ACP and 38spl dies. I gave another one to our #2 son in law in 40S&W & 38spl. They both are enjoying them and cranking out ammo like crazy.
If you don't have any dies at this time, it is a fine option for a beginner. Nothing says you are married to any of your presses and can get just about full price for them on the used market if you don't run in to a tight wad like me!
Now, I have one SDB on the bench right next to a Lee Classic Cast Turret Press and a Dillon XL650. That is that bench. On the other bench, I have a Dillon RL450B that has the new powder and primer modification next to a Dillon XL650.
Only one of those XL650s was bough new.
It really all depends on your needs. The RL550B is a good press and as has been stated can do rifle cartridges as well. The XL650 is as close to a production machine as you can get, the Hornady LNL AP seems to be in that same ballpark. Not for everyone. Personally, I like to be able to change out all of the dies in one move. But, since I have two presses, they just pretty much stay set up in the calibers I need most.
Check out the used market first. Dillon's warranty isn't negated because you buy them used.
FWIW