When I posted yesterday's assassin and monk classes on the ODD74 forums, it was pointed out that, unlike the assassin or thief's surprise attack, the monk's barehand attack could be used repeatedly. I think this isn't too unbalancing, since the monk risks things like petrifaction, contact poison, acid or slime coating, or just plain needing to get closer than someone using a weapon. But I can see how that might not be limited enough.
Fortunately, Delving Deeper has rules for striking to subdue (I'll be talking about them in my next DD critique article.) We can use these rules to put a limit on the monk's attacks: if the monk uses a barehand attack against an armored target, only subduing damage is done unless the monk's natural armor class is better than the target's armor.
Monks from 1st through 4th level have a natural armor class of 9. They do real injury against AC 9 or 8 opponents. They make barehand subdue attacks against AC 7 or better.
Monks from 5th through 9th level have a natural armor class of 5. They do real injury against AC 7 through 4. They make barehand subdue attacks against AC 3 and 2.
Monks of 10th level or better have a natural armor class of 3. They do real injury to any opponent except those harmed only by magic weapons.