No experience with the 550
Case feed is available for either after having one I wouldnt be without.
Caliber conversion from what has been said in other post is almost twice the price for the 650 as the 550.
Primer feed is kinda a pain to change out on the 650 but is simplified by having 2-650s one set up for small primer and the other for large primer
Best option is find someone willing to let you load on theres for an hour or so and let you get a feel for the differences.
Extras
Case feed- yes
Roller handle -yes
Strong mount -depends on how your bench height is set up
Bullet tray- depends on your set up. I prefer a box of bullets sitting on the bench reach in and grab a handful vs grab a handful and put them on the bullet tray one less step and one less expense. YMMV
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