Does the Martial Arts feat work with Teras Kasi abilities? I know (or at least, think) it doesn't work with the improved unarmed damage a Teras Kasi gets, but how about flurry of blows? Will the feat work with weapon focus/improved critical, even though it is (I think) a creature weapon? Will it work with dueling?

The feat does not appear to function properly right now, and it is not planned to be fixed to my knowledge, given the substantial bonuses monks already receive. It is more likely that the feat will simply be removed in the hak update. Some Bounty hunter feats are in the same boat. The bonus AB/Damage will likely be cleaned up, and the head shot feat most likely removed.

They are both situations in which the classes seem a little more balanced without those feats.

Being one of the few pure TK players that I know of, I can vouch for Daze's comments. Monks are just fine as they are, that said, don't take the feat unless you like shinies that do nothing helpful besides look shiny ^^

Like gold in Minecraft!