This is one of the best additions I have made to my 550:
https://www.amazon.com/JW-Systems-Di.../dp/B01L9Q2TX4
Much improved smoothness of the priming system. If you take the time to get it set up properly, and keep the slide area clean, you'll not have many problems with priming.
I put a flap of duct tape over the top edge of the primer catch cup, and the tag end down inside, to help direct primers into the cup, instead of bouncing on the top edge. A small magnet adds wight to the collapsible chute on the shell plate, which keeps it open to catch spent primers. I've also replaced the Dillon pin with a smaller diameter hunk of paperclip, to allow more free movement of the chute halves.
I added a .45 ACP case to the end of the primer magazine follower rod to add a small amount of weight, and help keep primers from flipping in the magazine if they are jostled by operating the press.
Edit to add: The roller handle is also well worth the money vs the stock round ball/lever.