One time I pak da'ed a guy who was holding a box cutter to my chest. It was the right technique for that situation. A pak da is a simultaneous pak sao (pushing away block using the palm of the hand) and straight punch. It looks kind of like
this. Note, I have no idea who that is a picture of, I just pulled it from Google Images.
Now I probably wouldn't pak da a guy throwing a punch at me in a fight (based on testing at an MMA gym*), but when his arm was already extended, and my arms were already kind of at shoulder height, elbows in (imagine a confused, "I don't know" type posture), it worked.
Of course, the criticism of TMA techniques is that they only work if your opponent leaves his arm extended. This guy did. But like I said, I probably wouldn't do it in a fight*.
The lesson here is to use what is appropriate at the time.
Fortunately the situation didn't escalate into anything bigger.
While I would probably not use WC techniques in a fight when I am already squared off against my opponent*, I have found that some WC techniques do work well for an initial response if you are just standing there and are startled by an attack out of nowhere. Not that that happens very often
*people are going to say "if you couldn't make it work then you obviously weren't doing it right"
(to which I would reply "if it works for you, then keep using it! It didn't work for me so I stopped using it.")