What's the pt for unsealing NM shield ?

as it doesnt give any bonus whatsoever ?

If you have the NM Heavy set it adds

Upper and lower body armor. Produces the following effects when worn with helm of nightmare, gloves of nightmare and boots of nightmare (heavy): P. Atk. +4%, Sleep and Hold Resistance +70%, CON+2, and DEX-2. With a shield of nightmare, 5% of the damage inflicted by the enemy will be reflected back upon him.

Also if you have Robes or whatnot you get pretty much nothing so dont bother unsealing it.