I've had a chance to play with this and it roughly reduces the status effects (KO, Stun, Shocked, Chilled) duration by half.
If you have this buff (for head slot) I recommend that you don't need to use KO and Stun resist anymore.
If you're looking to prevent Shocked stat, you can probably get away with just level 3 lighting resist. Since level 3 Ice resist is usually enough, you can go with either Ice/Lightning, or maybe even drop Ice altogether and get something like Wind resist or Fire resist, or Magic Defense/Defense.
Let me know if you want to set up a special match to see how effective it is.
Quick update: I was able to get this for warrior, and surprisingly not even through happy cards. I got it through spinners off of a level 7 premium item (the rocketman head piece). It doesn't seem to be super premium only. Good luck!
Thanks for the info Benihime. I got one for Cleric off of a premium (Psycho Head) myself, so it's definitely not super premium exclusive, although it was from happy cards not from the spinner.