Treasure Boxes must be opened with the deluxe keys that drop from mobs. Treasure chests can be opened with the unlock skill... beware, the chests may be empty, or mobs that look like treasure chests.
All in all, when your unlock skill is higher and uses fewer keys, then it can become worth the effort.
i would recommend to open only the boxes, cause if you are low at hp or somrthing you can be sure that you won't get attacked, and the chance to drop something in a box is higher than a chest ;)
All in all, when your unlock skill is higher and uses fewer keys, then it can become worth the effort.
I though that the Higher you go the More keys of thief you'd need?
That is correct. The higher your unlock, the more keys you need. Pretty silly for a thief, but can be explained with the lock getting so much more complicated.