One interesting note, this item doesn't work as description, it can shrink 2 giants if they're close enough to each others. Be careful, you may end up aggro 2 at the same time.
When you turn in the quest, this item will stay in your inventory. You can choose to delete it (no further use), or you can kill some more giants with it for the remaining time. edit: It appears you keep it even after the quest is finished AND the timer runs out, keep it to get those mean big elites to your own size and teach them a lesson!
Does anyone know if there's a way to get another one of these, if you weren't able to complete the quest in 2 hours? I'm afraid if I drop the quest and re-take it to get another one, all 12 of my residues will disappear...
EDIT: Confirmed. This is effectively a timed quest. You lose the residues if you don't complete it in 2 hours.