This spell is awesome. It can totally turn the fight in your favor if its a close match. When I solo, I have trouble with some yellows, until this spell. I can usually get it off twice during a fight. That is the equivalent of 2 swings of my mace. It's just free damage. No casting time. It does get resisted sometimes. If you are grouped and taking multiple mobs, it weakens them at the same time too. This can work well for you followed by the insta-cast mezz.
It's free, uninterruptable damage during commbat !! Don't look a gift horse in the mouth. This spell does wonders for me at level 8. =)