Pretty bad spell tbh (may be okay for pvp).
Problems:
Cast frostbolts, fireblasts and here's the kicker, polymorph. No matter what your spec is. People have complained that they are working on a mob that one mirror image decided to just sheep it (no reason, you don't have a petbar for them) thus healing it back up. The dps increase is minimal (as their spells don't hit for as hard as they did originally) and I believe can be easily killed.