The Dillon 550 is really a magnificent machine for its tight tolerances, ease of setup, durability, and simplicity.
Like I said, it all depends upon your needs, but the 550 is more than enough press for most avid shooters. When I first got my Dillon presses I was also skeptical of quality control. I had planned on just making 223 & 40 s&w on the 650. Then making only plinking AR-10, 44 mag, 45-70, 45acp, and 45 long COLT on the 550.
I was going to make my LR match AR-10 ammo and Varmint AR -15 ammo on my single stage presses along with hunting and F-class ammo. Turns out I was able to seat bullets and throw powder as accurately on the Dillon 550 as I could for my target/varmint AR loads on my rock chuckers and uniflow. I just got a conversion kit last week for my 10mm for the 550.
Now, the only things I load on single stage presses are my .300 win mag loads, .270 win, 6mm Ackley, and 30-06.
Keys to getting a 550 to maintain tolerances nearly as tight as a single stage include
1: Good dies....should go without saying but...
2: Selecting a powder that meters decently. Varget is about as long of powder as I throw, though 4064 doesn't seem to be sensitive to weight variation
3: get the shell plate sprocket bearing kit from level 10 innovations. It's $30 but allows you to keep the shell plate tight yet moving freely
4: polish the drop tube funnel with lapping compound or polish paste.....and spray the inside with scotch guard to avoid static electricity causing little ball powder grains from sticking
5: set the bullet seating die up with a case in the sizing station at the same time to ensure you are adjusting it for how it will be when you are actually loading.
And finally, do your load development on the Dillon. This way you don't have to try and recreate everything in the Dillon tool head you just did on a single stage. I throw my load development loads if I'm going to throw my loads I'm making. Why? Because I want to find out how well thrown loads group and meter before cranking out a couple thousand rounds.
Doing these simple things has ensured quality didn't fall with volume.