I just received a Square Deal last week after a few years of loading with a single stage. I decided to get the SDB over the 550 because of cost and I really only load 9mm so I don't have a need for loading rifle rounds. I figured if things change in the future it wouldn't be so horrible to have two presses.
I'm amazed at how fast this press can spit out rounds. I have no regrets with this purchase, my only regret is not buying enough components to keep it fed.