In Warlords of Draenor, this item will be added to the new Toy Box feature and no longer take up a bag slot. You will be able to "use" the item straight from the Toy Box interface.
The Toy Box will be account-wide and therefore so will this item.
The Mini Mana Bomb is a permanent item that was a Horde-only loot reward from the level 85 Theramore's Fall scenario. If the character faction changes to Alliance, the item will convert to Theramore Tabard.
what? i wanted a tabbard not this crap
And I've always wanted a miniature mana bomb (Fel Reaver, here I come!). No, actually, I agree with you - I would have liked the tabard because it's very nice looking.
But, it wouldn't make sense for the Theramore emblem (read: Alliance) to be available to/worn by Horde. The whole point of this lead-up to MoP is to emphasize that the situation is very ugly between the two factions, and will only become worse.