The Vortex was the first Discraft version of a Roc. One from '90 Worlds would be a very early run of them, so yours will be the old Pro Dish Competition plastic. Later the disc was switched to Tournament Pro plastic.
It's a pretty good disc. The Competition plastic ones were better than the Tourney Pro versions. The Tourney Pro ones were domey and flippy, the Competition plastic was a bit flatter and more stable. When I started playing, it was really the only mid Discraft made. Having said that, they were flipper than a Roc and really were never all that popular. So I'd say it worth tossing, but I don't expect that you will fall in love with it or anything.
Still, I think it's a cool find. If I saw one I'd pick it up. They have a pretty goofy wing on them. It's very concave, almost like the wing on the old Dolphins if you have ever seen one of those. Just for that I like to keep one around.