The double charge danger is pretty much restricted to pistol cartridges as a double charge of most rifle cases will leave a mess of powder on the bench.
Note: terminology again....the Dillon Square Deal is a fully progressive press. The Dillon 650 is a fully progressive press. The 550b is not; it is a semi-progressive press, manually indexed.
550B user here. All of those things are true. However if you use powders in your pistol loads that over flow in the event of a double charge, it is almost impossible to double charge. Since you place the bullet on the case with your hand before seating, now is a great time to put your eyes on the case and verify powder charge.
Manual Indexing is precisely why I chose the 550B. More control, faster/cheaper caliber conversions, easier to fix when something goes wrong.
What could possibly go wrong? If you are like me, you shoot on public ranges at least some of the time. When I sweep up my brass, I sweep up as much as I can get away with. That means everything.
At home I run it all through the brass sorting baskets I bought at Midway. These baskets are awesome. Worth their weight in gold. However, the baskets can’t tell the difference between 9mm Luger and 380 Auto. They can’t tell the difference between small and large primer 45 ACP. All that must be sorted out manually and invariably a few will be missed.
These odd cases will be easily found on your press during the loading process. That is when manual indexing pays off. Very easy to just back up, toss the bad case, set to the proper stage, and fix the problems.
I don’t use a case or bullet feeder. At a casual pace, I can easily load around 300-400 match quality cartridges per hour. I have literally loaded myself out of a job. I shoot a lot and can’t stay ahead of my 550B. I have long ago ran out of storage and just started using 50 cal ammo cans to store bulk pistol ammo.
Even if I shot one practice round per day, and one league match per day (which I don’t/can’t), I could load up a weeks worth of ammo in about two hours.
But if you need a higher loading rate, by all means, go with a fully progressive press. I don’t think you can go wrong with Dillon or Hornady.