starting new to reloading i would recommend the 550. it is user friendly and you can stay at one station, bullet seating for example, until you get it where you want it then do another station until its completed to your satisfaction. the 650 will index it around everytime you pull the handle and you can't back up. if you want to do multiple calibers, buy antoher toolhead and put other set of dies in it and just change out toolheads when you change calibers, except for maybe large to small primers. anyway i have worked with both and 550 is extremely user friendly. learn on this and then maybe step up larger later after you have become proficient. hope this makes sense