The glottis breathing is done in yoga and the instructor explained how to do it as- constrict your throat as though you are going to make Darth Vader noises. That helped a lot of people get it.
I used to play horn but I don't remember using glottis breathing, at least not consciously.
When teaching singing I show students the heavy breathing Darth Vader sound - to illustrate what we DON'T want. Which is false vocal folds restricting the air flow through the glottis.
Doing this habitually will force your true (and precious) vocal folds to work harder to make a nice sound and you will damage them.
Interested in Linda's experience of mouthing words being bad. I can see that - thanks for the heads up!