My first press a Lyman SparT. Still have and use. 2nd SDB, sold after 7yrs use. 3rd RL550B, 4th RCBS Rockchucker(old one). I still use the 3 I have. Each has a valid reloading use at different times. I.E., the rockchucker is good for resizing .308 cases fired in an M1A. Takes more resizing effort than feels comfortable on a lessor press. Just my view get what you need to get to do the intended job. That being said you can use a 550 as a single stage, a primer unit only, size and primer only or as intended as a progressive just depends on your particular need at the time.