Their use is mostly pain; i've never actually seen anyone use them for anything other than consussing people in real martial arts. [Ok, you can, disarm stuff but it's not great to pit chain against a blade and it requires two hands]
I know they were given the disarm bonus in core but i'd either up their damage or give them a bonus on attacks of opportunity [if you can price that at a 1 slot, +2 to hit maybe?] because they're fast and really difficult to block.
If you go with the attacks of opportunity thing, another really fast weapon is the hanbo, which is basically a club wielded in a different way. Monk weapon, pretty solid defensively and fast.