Spider Sponge Care

[Mangodude]

So I'm pretty much a newbie to this whole NPS thing. I have cup corals and have had sun corals. I have tubastrea's and gorgonian's so feeding the tank specificly for the corals isn't a problem.

I've got the opportunity to buy one of these for $30. Debating whether or not I should give it a shot..

I know these are difficult to keep but I would like to know what specificly makes them difficult. I don't mind a challenge..