In response to your question.
Mem Blur is hard to resist and is useful for a fight that went really bad with a non aggro critter.
Like Mez it only works with a coordinated group that wont continue attacking.
Like most spells at the level you get it the thing fizziles too often and costs too much mana. However later on you can easily have that much mana left when you realize the fight will go very bad.

Use Mem Blur to make the target forget who he was mad at and then the fight might be over as he wanders off and you or your group recover.
Use it the same way to break up trains. Even on aggro or assists it stops them for a second or two and that can give the fleeing people the extra edge to get away. Sometimes if you hit the trailing edge of a train or a slow critter then they just wander off isntead of hearing the cries for assist or seeingthe target in thier aggro range.

Use Mem Blur to pull a monster off a Tank or anyone else who it has frenzied on and is getting pummeled. Just tell them to stop attacking, Mem Blur and then it will go after whomever hits it next or is naturally high on it's hate list.
I have saved several clerics, wizards, tanks, and myself with that use.

Stonedreamer