I love my 301's and use them all of the time. I have 2 at the moment -- each with carrying case. I would question the owner about only 1 bobbin and no attachments. Slant attachments are not hard to find, but I certainly would have thought that doing upholstery, he would have had the need for a zipper foot to get close to piping. And the 301 bobbins don't hold a lot of thread, so only one bobbin for his kind of work would have been inconvenient.
301's do seem to be increasing in favor and price.
Another thing -- I use an older Singer slant walking foot with no problem, although I don't think the one I have was made for the narrow feed dogs.