I really don't think that Power Attack is very useful for Monks. Your attack bonus is just so low that unless your damage is terrible (in which case, yes, power attack might be good, but it is only because your character is really bad), the vast majority of opponents will have ACs too high to make power attack worth it.
Cleave has a different problem- your damage/swing and attack bonus are both low compared to a 2-handed wielder type, so getting an extra attack is worth a lot less to you.
Cleave has a different problem- your damage/swing and attack bonus are both low compared to a 2-handed wielder type, so getting an extra attack is worth a lot less to you.