Breathing techniques and the Tibetan/tummo techniques ?

Breathing techniques and the Tibetan/tummo techniques ? I've been reading a book called "Breath - The new science of a lost art" by James Nestor. It's all about breathing and how it can have drastic affects on the body and different techniques can have different benefits on the body. A famous example is Wim Hof who practices these breathing techniques and has been able to withstand intense temperature changes, altitudes, exercises and even diseases such as when he was injected with ecoli. These techniques have claims of fixing, if not curing autoimmune diseases and such. I wonder if anyone in this subreddit has tried these specific or similar breathing exercises and have they had any affect on your stutter or wellbeing ? They same relatively easy to get the hang of but difficult to master and there are multiple paid courses to better learn these techniques but I don't want to pay so much for something if it doesn't have an affect on the stutter or mind.