Yep.. They are one of 3 items you get by defeating the Dark Knight, which can only be done by starting a new char in the KR client. Only one reward per character, and the quest is kind of still bugged so if you fail to recall off the rune the first time you try to challenge the Dark Knight you will never get in.
This particular item is pretty much only one that is worth while. When carried and turned on, it will tell you if you are doing the right activity or fighting right monster for skill gains. Anytime it does a skill check it tells you if it was too easy, easy, optimal, challenging or too challenging.
Most skills have skill guides available so not really needed, but not bad to have. I recently used mine to determine best armor to wear to train stealthing.
