There is a hidden zone requirement for using this item. I tried to consume it while in a raid instance and received the game error, "You are in the wrong zone." :|
I tried using it while at Darkmoon Island (I went to get the rep buff first), but it returned the same error. I returned to Mulgore; same result. Went back to Draenor, and whaddaya know -- it worked.
I guess it's just as well, or I might not have gotten the rep bonus from my Level 3 Trading Post.