It does it thing by explaining emergency techniques and difficulties that might arise. But to be a practical book it feels very theoretically. If I say victim to a patient that is stable on the ground, who cares? Does it matter if I can tell which lung issue or DCI the patient have if the treatment is the same? The book could probably be around ~30-50 pages to contain the key information and more than that, but it would be hard to sell for 50 $.
Also with explaining how to tow a victim in the water and bring them up from the water sounds easy. In reality, if diving in cold conditions and the guy is having a drysuit, double tanks, weighing 100 kg + 50 kg equipment, how the fu*k am I going to carry + my own equipment? At least 3 people will be needed, that is why it boils down to judgment, you should never come to this situation cause if you do, you shit will hit the fan.
In the end, the more you know, the better you can handle situations that can arise, you might save a life. That is the reason I don't give a lower score, I hope I will never need to use the knowledge.