These are unproven techniques based on retelling/modifications of ancient techniques from Pranayama - https://en.wikipedia.org/wiki/Pranayama

Yes, i have read James Nestor's book "Breath" and did not find it illuminating.

A better way is to read some good books explaining the techniques of Pranayama. There are plenty (the two books "Prana and Pranayama", "Prana Vidya" published by Yoga Publications Trust, Munger, Bihar, India are good) so buy a few which appeal to you.

Here are some suggestions (based on my practice);

1) Do not practise the breathing exercises when you are feeling hungry, too full, tired, hyper, sleepy etc. Your practice should be done only when you are feeling comfortable and calm.

2) Do the exercises in a well ventilated place.

3) Do not do any breath holding exercises in the beginning for at least a few months. You should only practise inhalation/exhalation with various lengths and force as prescribed in the techniques.

4) Generally, the ratio of lengths of Inhalataion:Exhalation should be 1:2

5) Generally, Inhalation/Exhalation should be "subtle" and in a "thin stream" unless the technique calls for force, but should not hurt the nostrils.

6) Both before and after the practice massage your whole body lightly with your hands; particularly the forehead, eyebrow ridge, temples, and the scalp.

7) The following techniques are enough to give you immediate benefits; a) Kapalabhati b) Bhastrika c) Nadi shodana (alternate nostril breathing) d) Deep Inhalation through the Nose followed by slow Exhalation through the Nose e) Deep Inhalation through the Nose followed by slow Exhalation through the Mouth. Note: The first two will clear your sinuses/nostrils and energize you making the subsequent ones easy, the third one will stabilize and integrate you, and the last two return you to relaxed and calm mode.

Finally, you can use a Blood Pressure Monitor/Pulse Oximeter/Spirometer etc. to monitor/measure your physiological parameters both before and after practice.