I was using a Dillon 550 when I was loading for 9mm for USPSA. It worked great but after some time I wish I had invested in the 650 for the extra speed.
For checking powder drops I've read people will mount a small mirror to see into that station. I don't feel I needed it on the 550, it was something I would check before I rotated.
I have some extra 223 dies and a few other small items I'd sell pretty cheap if you're interested, I really just want to get it out of my old bench.
Enos was the place to buy when I purchased but I don't think he's selling them anymore. I think bobcat armory or bobcat steel or something like that is a good place to look when b purchasing. He has trade in units for sale all the time as well as new stock.
As mentioned, the FA primer tool is great, extra primer tubes, multiple toolhead set ups.
Inline fabrication has some cool stuff to look at as well for accessory add one.