If your intent is to spam it and negate all damage, then yeah, the MP cost is going to hurt. As a 'use once in a while' to get out of a tricky situation I don't think it's terrible. That being said, a lower MP cost would not hurt or overpower it.
My first thought when I used it was that I wouldn't mind seeing a lower damage threshold before it 'breaks' and just eliminate the timer all together, but I think that also falls under the consideration of whether you're trying to use it as a blanket vs. a quick defense.