I heard few times that 550 is more manual then 650. Been using 550 for a while and closely looked at 650, the only difference is that 650 gives automatic indexing between stages, so you don't have to manually turn the turret. That should speed up the loading process a little, but can also increase chances for mistake, e.g. can stroke the press twice and produce a round without the powder (squib). Can someone elaborate on where is an additional complexity in 650?
I am thinking of moving from 550 to 650, but mainly because I want to get a bullet feeder and get to 600..800 rounds per hour loading rate.