I have the FD-8.
I skimmed over the posts, above, so don't crucify me if I'm repeating. Usually JR97 covers all of what I'd say.
The FD-8 is a nice machine, with MINIMAL menus, & a full analog mixer. BUT, it will only record 2 tracks simultaneously, unless you have an ADAT-I/O compatible mixer, THEN it will record 8-simul. The FD-8 is best to be found with an internal hard disc already mounted, if possible. It's a really good sounding, versatile unit. There's 24 internal tracks, of which only 8 can play back at once, so there's an "alternate" track scheme, in which you can trade tracks back & forth, for different purposes. The little LCD meter & menu section is not the greatest, as LCD's are not my favorite anyway, but at least it's backlit, so that's a plus.
The FD-8's a great unit, especially as compared to the new MR-8, based on features alone. It's well worth the average used cost of $300, with hard disc included. It's a good unit for someone who wants that 16/44.1 digital image data, with the look and feel of an analog porta-studio. The greatest limitation, as I see it, is that it records only 2-simul, but if you work alone, [like me], it's really not a hinderance. Any larger group recording ambitions, and it could cramp your style, and necessitate the ADAT-I/O type mixer, of which Fostex made many, from the VM-200 to the VM-800, the one's I'm most familiar with.