The 500 is a modernized version of the 401 - it's a slant-needle machine with many built-in stitches and more designs available on cams.
The cams, accessories and many replacement parts are easily available.
In my collecting days, I'd have jumped on this one, and in fact, I did. I gave it a good cleaning inside and out, oiled it up, got it sewing well, replaced the bobbin winder tire and LED light bulb and gave it to my daughter. It's a really nice sewing machine,