Conceal Spell is naaaassty hard to use, as written.
1) Say you want to feint. Okay, fine, roll to feint. Then, roll to actually _hit_. Succeed at two checks or nothing happens. Feinting is basically terrible, but if you have a massive Bluff bonus, you can perhaps skate with it.
2) Say you want to Conceal a Spell. Okay, fine, the other guy rolls his _highest_ of 3 different skills, and you hope he fails. Then, he rolls a saving throw. Will negates? Crap!
Want to have an easier time concealing your spell? Figure out how to reduce the bonus of _3 different skills_ for _everyone in the room_, rather than just boosting one skill of your own. Good luck!
Oh, yeah, if you're a mesmerist there's a bold stare or two that can reduce _one_ of those skills (Perception) for _one_ person. Good luck!
Cunning Caster is massively superior. This is why it isn't PFS legal