I've only used silkspan, so I'm just regurgitating things I've read:
Yes, the CF veil is for solid wood; it adds more strength than silkspan for the weight (and it's a bit tricky to apply -- apparently you want to brush it with dope once and then stop until it dries -- if you go over it too many times when it's wet it'll stick to your brush).
I've used stuff called "Polyspan" on little RC models, but I'm not sure if it's exactly the same. It's sort of a plastic alternative to silkspan -- it doesn't go around corners as well, but it covers open-bay structures nicely.
Polyspan is for open bays; folks that use it either use silkspan or CF veil on solid expanses of wood.
There. If that's not everything I know, it's more than I actually know.