Ive heard that if you get the yonkajo point on perfectly, you feel nothing in your wrist, but your knees give way.
Hmm pressure points. One of the sensei's that taught me used to do this one from a shomen tsuki (front punch), he would enter then press on 2 points on either side of the rib cage again your knees just give way and you fall to the floor. I think the location id about 4 inches down from the arm pits. I have difficulty getting it just right though.
I have seen videos of a sensei, I will visit in June who performs a one armed hiji ate. As the punch comes in he taps the elbow joint with perfect timing and you go flying (its great). The problem is that it is a difficult one to practice, as if you get it perfectly the elbow joint breaks. Its a difficult tecnique to exercise control.
If you read Total Aikido-by Gozo Shioda, there are pictures of him demonstrating it there.
The one your sensei did sounds really nice, grabbing the neck etc, Ill have to try it in training.