Estimating FTP from 20 min power is Hunter’s approach, not mine.
That said, on average 95% of maximal 20 min power agrees with the WKO4 model prediction.
The “on average” part is one reason why I have never been a big fan of this approach, because why go to all the trouble of a formal test when you can (mis)estimate FTP just as (in)accurately using other, informal approaches?
The other concern I have with the approach is the 5 min “blowout” effort. The one study of which I am aware that tested the effect of this surprisingly reported that it makes no difference. However, if you truly do go all-out for 5 min, it’s hard to pick yourself up off the floor, much less follow it with a decent maximal 20 min effort. So, how hard should you really go for those 5 min, and what if the quality of that effort varies from one occasion to another?
Finally, re. the link you posted: at least based on the title, it appears that the authors don’t really understand the concept of FTP. I therefore wouldn’t put much stock in the actual content.
ETA: Sorry, I couldn’t help myself…since when does multiple regression count as “AI”?!?