I honestly think Pain Touch is a great ability for any Monk to have, as long, of course, as that Monk utilizes their Stunning Fist ability often. It really does, if you look at it, double the Stun you inflict, although under a different name of nausia. It also leaves a Monk's next turn free to use a Stunning Fist on someone else if desired, against two different foes, if you keep one stunned and the other nausiated in sync, you can easily take down two at once, in theory, anyway.
As long as you have the WIS, I don't see any reason at all not to take this Feat.