Is there a quick way to unequip a spent Mantle?
Solution 1:
Mantles will also automatically unequip if spent when your hunter sheaths their weapon after combat.
Solution 2:
Yes, if you just use the item again the Hunter will unequip it and the cooldown will begin.
Be careful though, because if you put the mantle on and then quickly take it off again, you still have to wait the full cooldown.
Other than just using the nav-wheel, there is no way to automatically take it off when it expires (right now... this could change, or be an armor skill later on)