Well, I can tell you lots of things I love about mine. Others have mentioned the excellent quality of the straight stitch And it's portability. The other things that come to mind are that there are some really fun attachments you can add to it to make it do all kinds of things besides straight stitch. For example, Singer made a zig zag attachment that foes on the foot and has cams it moves the fabric under the needle and you can do about 8 or 10 decorative stitches with it. I have one and have had great fun playing with it on my 1955fw. There's also a buttonhole attachment with cams, I have that one too. And there is a fellow who sells a modern hand crank and gives very clear instructions on how to switch your FW back and forth between a hand cranked machine and electric. I have one of those too and it's a lot of fun to just do the conversion(takes me about 15 min) and take my FW outside and sew away under a tree in the park.
If you use it for chain piecing you won't miss the thread cutter.
I don't know what ones that have been completely restored run, but if the person is asking $200-$300 I would expect it to have its bobbin case (check, they're often missing and I've seen lots of folks reporting that the reproduction bobbin cases don't work as well in the pre1960s fws. You can sometimes find an original bobbin case on eBay for $30 ( if you're lucky) but I've seen people get into bidding wars over them as well and it can cost lots more to get an original one as a result.
i got mine at a junk store for $60 (no case, but lots of attachments) oiled it, cleaned it and it ran fine, no tension problems at all.
Rob