I have a Craftsman sander almost identical to that one. My primary need was the disc sander and the 6 inch worked for me for awhile but was undersized and the aluminum table seems a bit flimsy, which makes it hard to keep dish and table at 90 degree angle. I replaced it with a 12" Delta disc sander. :biggrin:
In my opinion if it was $79 you should consider it as a starter.... but For that kind of money, if you are looking just for a disc sander, I would look at dedicated 10 or 12 inch ones.
I have one like that only a few years older. The disk isn't as flimsy as the cheaper ones with 6" disks. I built a squaring jig that works very well.
Having said that, I agree with Lenny. If you only need the disk, go for a dedicated 10 or 12" model.