SummerRain,
yes, most exercises are variations of the abdominal breathing.
I found the basic one you described most helpful.
When I was in bad pain last year, this was the only exercise I could tolerate. I would just lie down on the floor and do it all day.

After a couple of weeks I noticed that 20 minutes of breathing provided an hour or so of relief and that I can make it through the day by doing it every hour.

The other exercises I found helpful was the longus colli strengthening and the foam roll. Breathing on a ball - not so much.

I think in my case TOS symptoms are secondary to RSI. My overworked neck muscles were constantly spasming causing pain due to nerve compression and trigger points. Doing Edgelow's exercises alllowed the muscles to relax and take pressure off the nerves.

I don't think they helped much with trigger points as I still have a lot of myofascial pain in the neck.