Tome of battle can be very OP, though less so in PF than it was in 3.5 so keep a close eye on their character builds, especially the Crusader. Crusader with the right load-out can sac turn attempts(Pos eng burst now) in order to re-pull use abilities, pair that with the ability that let's you choose someone else to take an immediate action, means that your strats against the party can be turned upside like nothing. A buddy of mine and myself played two Crusaders who used these abilities back to back to spam free turns for ourselves/allies. With a couple extra Cleric levels under our belts we had plenty of turn attempts to fuel the re-pulls of the immediate action ability. It got really cheezy really fast lol.