I owned a SD-B for 20 years before upgrading to a Dillon 650XL. While the SD-B is a competent little Press it limits you to using their proprietary Dies only, pistol calibers only, and is somewhat uncomfortable to the user when loading during long sessions.
The 650 has since been replaced by the 750 and can use any standard Dies, is so much faster, allows an auto case feeder to be use, can use almost any brand of Dies and is so effortless and comfortable even while loading 3,000 - 4,000 cases at a time.
If you are spending money on a Reloading outfit I would strongly urge you to go for the best right away and not have to deal with upgrading shortly down the road when you might want to reload calibers not applicable to the SD-B. Comfort and ease of loading as well as speed and efficiencY are important to me and the SD-B just can't live up to that IMHO. Yes it will get the job done, but in the long run it's not the best way to go.
PS: Changing Die's in the 750 is a piece of cake! Especially when the Die Blocks and extra powder canisters are used.