For me - as a pax and enthusiast - there are only 2 explanations for what I get to read here
a) after all these years in an industry full of rules, regulations and safety concerns still nobody has enough data on performance on contaminated runways, especially on performance difference between manual and auto braking
b) there is not much difference between the two methods and it is at pilots (airline?) discretion, especially with the possibility of using both (with timing based on experience being crucial)
I hope someone can confirm it's b) or some c) I have overlooked
