One of the things I've been suspicious of is that just retraining the voice may actually damage the vocal cords, especially related to significant pitch changes. Anjaq's issues with her vocal cords may be evidence of that.
Personally, I've mostly got my male resonance under control, so much so that I find it hard to put male resonance back in when I'm presenting male (still not full time). I'm usually ok if I don't try to suppress resonance early in the day but once I've done that for a few hours going back to a "male" voice is really a struggle.
Even so, it's when I attempt to raise pitch, since that vocal cord of mine forces all the work to the single "working" vocal cord, that I get tired much more easily and my voice cracks easily. And sometimes the throat hurts when I've done that so I don't push it too much. Despite that, after a good year of effort, raising pitch is still problematic for me though suppressing male resonance comes naturally and even without a significantly higher pitch I am being gendered occasionally female on the phone.
Consequently, I am wondering if the Yeson method (is that a term? should it be?

) will become far more popular going forward? It sure seems like it might.