The CM Pro isn't Costar, but the linked one in the post is.

They keys are a bit nicer on the Filco and there are also more mods and replacement parts available for it (yay, aluminum bodies). The Filco PCBs are a bit better: "the through-holes for the switch pins has pads only on the top surface for CM, while Filco has pads that are on the top surface and goes all the way inside the holes. The trace/pads are less prone to being ripped out, but of course this probably only affects desoldering."

On top of that, Diatec (Filco) has great customer support and has been known to send their customers replacement parts long out of warranty.

I've heard that argument too, but so does Rosewill and there are definitely some quality issues there; that's certainly up for debate though. Some might also call Filco overpriced, but I've certainly never heard that about a WASD board.