Ok, assuming a 6th level Monk already has Improved Grapple and Deflect Arrows, what's left?
Catch Off-Guard, Scorpion Style, Gorgon's Fist and Throw Anything all suck. Improved Bull Rush, Improved Disarm, Improved Trip aren't the focus of this character, so they don't seem like great choices. Combat Reflexes and Mobility don't fit the character's combat style and Dodge doesn't really seem worth a feat.
Hamatulatsu seems to be the best choice, though it's only slightly better than a cestus when you crit.
Am I missing something?