Yeah I would not teach to neck rein in the hackamore.
I love to show in one on a junior horse, however I know a lot of people do not know how to use one properly and have indeed made their horses hard in the face. My gelding is an example, he came to me "hackamore broke" whatever they meant by that, and was bracey, hard in the face, pushy, no respect for it at all, couldn't get him stopped or listening at all. Three years later, he can be ridden in one again. It is far easier to play it safe than to put a horse in equipment like that unsurely and ruin him, because then someone will have to rebuild it.
So, if you choose to go that route, have a trainer help you out. That's my advice anyhow.
Pssh.I didn't pick up the wrong lead
It's called a counter canter...
...A very advanced maneuver.