Very great mod. Thank you very much. "Buy perk" side effect - is nothing compare to awesome feature this mod gives. But, it wil be "the best mod ever" if we(you & all community) could add some other such "mastery skills", like athletics(run) and acrobatics(jump), healing mastery(heals&meds) , armor mastery(damage reduction), or even some skills like bonus damage to animals, zombies, etc