To be honest with the new content and how powerful magic is now, it may be of more use then it has been previously, Since the dark magic's take a lot of stamina to block, do magic damage and are very popular, this seems like the perfect spell to counter them
It will never be useful because of the terrible duration of like 25 seconds. Its never worth using like that. It won't out last a buff or be extremely helpful. If you could choose weapon buff or shield buff at the start of a duel, I know which one I'd take, just for that reason.