I'm not aware of anybody with a high profile performing career who has adopted the whole Postlewate approach.
The article cited above seems very balanced, but then it was by Colin Cooper, who got most things right. Though the article cites Aguado mentions this usage, does anybody have any idea about that?
The book is the one by Postlewate.
Postlewate was kind enough to send me all his publications and recordings after I'd made some reference to this in CG magazine. To be honest, I felt that the one thing that undermined the whole enterprise, as it was presented by Postlewate was that the tone he was making was distinctly poor, and close reference to the DVD suggested this was because in order to include the little finger all the time, his RH position was extremely low, impairing the action of the other fingers. Obviously that is a limited amount of information upon which to form a view as to the whys and wherefores.
One could get in touch with Postlewate easily enough and ask direct if he does Skype.
I use all 5 in chords such as the end of Villa Lobos Prelude 4, and the little finger for artificial harmonics. I did years ago have a student who had self-taught, and like Villa Lobos, had seen little reason not to use it.
Simon Ambridge Series 40 (2005)
Trevor Semple Series 88 (1992)
Louis Panormo (1838)
Alexander Batov Baroque Guitar (2013)