A Dillon 550 can be run as a single stage press one case at a time. The Internet is filled with Lee progressive press horror stories. For every Lee owner that never has (or has very few) problems, there are 95 other owners that wish they had bought another brand of press.
Dillon customer service is #1, responsive, correct, life time warranty. Yes a Dillon press will wear out parts. Aluminum does not have a infinite fatigue life like carbon steel. Eventually a repeating load will crack an aluminum part because aluminum work hardens and becomes brittle. I am on my 4th ram pivot / handle bracket for my 1982 Dillon RL 450.
Dillons just work. Read the owner's manual and 98% of the problems are covered. Cleaning the primer arm and lubrication of moving parts are all that's needed -- no tinkering required.
I have a Dillon 450, 550, two RCBS RockChuckers, and a Lee entry level press that is used for seating bullets at the range. The Lee struggles to resize 38 special brass with a carbide sizer die. Lee is a 3-letter word for junk. I've worn out enough Lee equipment to have that opinion. New oats always cost more then old oats from the horse.