But that's exactly what this man is demanding !!!
And if you want to dive deep, you have to train your ability to perform a CESA.
In the 1970s in Germany, an advanced diving certification included a free ascent from 30 m. This part of the test was removed because there were too many incidents.
At that time, we had a maximum ascent rate of 18 m/min, so the ascent only needed 1.5 minutes.
As a freediver, that was also a fun exercise for me. Back then, and even today, I believe that a minimum level of freediving ability is part of advanced scuba diving. Let's say a freediving depth of 18 m should not be difficult, then a CESA from 18 m is also not a problem.
Before the 30 m free ascent, a free dive to at least 20 m should always have been demonstrated first.
If the problem is that you have emptied your tank, for example in 50 meters, it still has 6 bar of pressure that you can use when ascending to a shallower depth. You can calculate an acceptable ascent, and you can also try it, which I have done. However, I would only recommend trying it to freedivers, as it is quite challenging.
I don't know if the exercises suggested by the man are very helpful. This is not mainly about learning movement patterns, but about physiological adjustments when one cannot breathe. For comparison, one does not learn long-distance running in a few days , but through frequent training the body adapts without us having direct influence . You should be happy, calm, and relaxed, even if you sometimes don't need to breathe or can't breathe . The redundancy you gain from this is sufficient for most recreational dives.