45C: The 550 is a more versatile press. You can reload a large variety of cartridges on it, including many rifle calibers. The 550 also allows the use of any standard 7/8 X 14 reloading die....unlike the Square Deal.
I owned a Square Deal for some time. Then, switched over to a 550 in the 1980's, as my reloading needs broadened. Have since loaded many thousands of rounds in various calibers, without issue. The press has run trouble-free throughout, requiring only regular maintenance. It still gets used regularly. Far more than all my other presses combined.
I don't mind the manual indexing, at all. Makes it easy to stop and trouble shoot problems if they arise. Caliber swaps are equally simple. Pre-set dies can be mounted on tool heads...which are easily changed out, in seconds. Then, change out the primer ram and primer tube(if needed) and shell plate. That's about it. An entire caliber change is easily achievable, within 5-10 minutes.
Even if your reloading volume is fairly low, the 550 is ....at least in my opinion....a good long term investment, for any reloader.
My .02 Cents:
Al
ps: Changing out .45 ACP from large to small primers is pretty simple, too. Only takes about 5 minutes. Biggest pain is sorting out the brass(If range pickups).. Some shooters hate the .45 ACP brass with small primer pockets.
I like them. Makes caliber changes, ie: .45 ACP, 9mm, .40 S&W, .38/.357 etc., dead simple.