I went with multiple Square Deals - I like auto indexing, it's one less thing I have to do. I started out with one in 38/357 and then bought a tool head for 9mm. I didn't like changing them around, so I bought a couple more Square Deals (I shoot 45 acp a lot these days). I have a 650 for non-pistol calibers. Not owning a 550 - I'd assume you have to swap out not only the toolhead but the shellplate also? Does the primer feed mechanism get swapped too on the 550?(if you're changing from small to large primers).