I have a level 12 party, and am just about to set off to the Underdark. I wouldn't mind having Celestial Fury with me when I go, as I have heard it is one of the best weapons in the game. Do you think I am high enough level to take them on yet?

deffinatly, i normally go at level 10

I don't think it's nearly as bad as it was first made out to be on these boards. You should be fine. If it gets tough, head back down the stairs and the enemy party will split up and some will follow you.