I had not seen the update but it aligns with my thinking that longitudinal monitoring might be useful. I knew he had issues with the statistics and generalizations. I found I am an outlier and that these limits do not come close to any real physiological break points in most cases.
DFA a1 is still an interesting thing but I think it is not as simple as has been reported to date.
Have a look at the alphaHRV app on the Garmin IQ. store. A couple of Spanish academics have been working on it and seem to having some success identifying the first ventilatory threshold by using the Respiratory Rate and DFA Alpha1 combined. There are long and involved discussions on it on the Intervals.icu forum.
I have tried the alphaHRV app but on my FR 255 it will only work in ANT+ mode even though I can link my Polar H9 in BT to the watch. I think there are some persons who the Alpha 1 works for and others like me it maybe does not or I am a strange case? I find it interesting to watch though since it seems that with time it may have ways to tell me something if I track it long enough.
DFA Alpha1 works for me. It basically confirmed the talk test and also hits the middle of my WKo5 zone 2.
I listened to Bruce Rogers on many podcasts and have read his site a bit:
One thing that seems certain is that you have to use a Polar heart rate monitor for this. All the other are just toys compared to Polar. Polar is the only one validated for scientific experiments. And you especially cannot use an optical HR sensor.
It’s a big rabbit hole to jump down. Or one could just use the talk test, your zone 2 power, and call it a day. 
One thing that playing around with DFA Alpha1 showed me was that my aerobic threshold was around 130bpm when I was fresh and rested and more like 120bpm when tired. Typically, I just use 125bpm for Z2 intervals.
The new version of it doesn’t use the 0.75 and 0.5 values for the thresholds as they would appear to be more a population average and thus not much use on an individual basis (A bit like HRmax=22-age). This is the long thread on the forum about it if you are interested.
