So, if I want to get into Warhammer Fantasy, do I need the GW minis, or can I buy units from Mantic Games or other online retailers with generic fantasy minis and use them?

Specifically, I'm looking at these elves http://www.manticgames.com/Shop-Home/Elves.html for use as High Elves. It definitely seems like they were designed to be used as high elves, but I'm a total new GW player, so I could use some guidance.