Came across this recently. Basically you attempt to verify your FTP (CP) by launching into an all-out 3 (later shortened to 2) minute effort immediately after the end of a ramp test. Painful, but it seems that it works.
To me, the group is too small (also age wise) to draw conclusions die everyone…
After doing long tempo/sst and FTP blocks, I now “feel” where my FTP is. It is lees painfull 
That would be awesome if it provided more accurate estimations, but I looked at the detailed method, and oh my, painful is an understatement!