I just got my 550 in yesterday, and got it set up.While I was waiting I ordered a couple of add ons. Heres my take on them.
1. The led light for the inside of press.This gives out more light than I originally thought once in place. With correct placement it shines right down in the case.
2. Spent primer cupI replaced it with one that is basically a funnel that a hose attaches to it that drains into a bottle. This is of the two much better, it allows me to not have to worry about the cup and does a great job of catching primers.