The Warp Slicer item (legendary item from Kael'thas in the Eye) is appearing as collectible even though it cannot be transmoged or anything. If I equip it, it does nothing. Is this intended?

Below is an image of the item so I can use it to explain what is going on here. In the image you see that it is listed in ATT as any piece of gear that has a sourceID we want to list. Some items are special while others are straight forward. Your straight forward gear is normal pieces of gear. Then you have some that can be learned, but not transmoggable (Steins, Fish, Shanks, etc) which are shown but need a Shift+click to get the signal from Blizzard.

Then you have items from Tempest Keep that are similar to this in that they can't be transmogged. When you look at the item you should see the text "This item has a Source ID (Tempest Keep Legendaries), but can't be learned (training recipes)."

Usually when there is red text like that on an item there is a filter associated with this. This basically tells you that it has a flag on it that is currently turned off (Artifacts had this same thing) and no matter what you can't learn it. Due to this you typically won't want to see it. If that is the case you can go to the second Tab Account Filters and scroll down to Training Recipes / Unlearnable (15) under the header of Unobtainable (Check to hide). This will cause it to no longer show up in your list, but when you loot the item it will still have the text on it.

Hopefully this helps clear the reasoning behind it up some.