This quest does get you a daedra artifact but it is much harder. But I can't tell you where the thieves are for I am not a high enough level. But if you want a fun daedra quest with a useless weapon do the sheograth one. There is another fun one that strips one of the countesses down to her underwear but I forget where that is.
Murphy's Law: It is impossible to make anything foolproof because fools are so ingenious.