So i took a few photos of the Forbidden Stars figures so that people can compare scales
Orks

Chaos

Eldar

Marines

Scenery

So overall we can see that a few things are quite promising. The Battlewagons and Falcons are pretty good matches, the Land Raider isn't too bad, though it is a little small, and the Hellbrute is too big, but not by so much that it couldn't work
The Titan units are all much too small to be titans, but the Gargant is pretty much spot on for Stompa size, and the Warlock Titan could make a very nice Eldar Knight/Wraithknight. The other two are a bit less so, though the reaver could work for a knight of some sort. The Warlord though, I think is too distinctive, but would make excellent statues.
The Escorts are pretty close to BFG size, but the Cruisers are tiny (they are really too small for anything other than heavy escorts, or just an alternate build escort, though it's been pointed out to me that the marine Strike Cruiser is also pretty tiny, so it may match up. The ork ones in particular would obviously make good conversion fodder)
That said, what the ships are excellent for, is to use as spaceship markers for Epic, where the scale is irrelevant already.
The scenery is all too small, though the Bastion is not so much as to be a problem (it's about the same size dysmorphia as the titans and SG aircraft are) the other two would just have to make do as bits, or campaign tokens
Speaking of Campaign Markers, I didn't bother to take photos of the two flag/icon options for the various factions. they are visible enough in the earlier pictures, and can be figured out for scale via the stuff i did photograph. They'd make pretty great Blitz (bigger) and Regular (smaller) Objective markers though, or of course, campaign tokens.
Overall, the models are pretty good. they're not up to GW standards as far as casting goes, but with some paint, they wouldn't look too out of place (especially if not taken alongside the actual falcon or land raiders for example) So i think for Epic, they're not a bad buy. Less of a deal for BFG though.