Really glad I found this thread about 18 months ago. I have the PLB A flex in my Ping 400 Max driver and in my Ping 425 fairway. Very happy with the results although I am wondering about going to the L flex and perhaps a 425Max head. Hitting the ball longer and with a nice draw. Definitely a believer.
Have you seen the latest from the Autoflex company? It's called Freeflex /Metaflex and brings a whole new dimension to shaft manufacturing. I'm not an engineer but my understanding is there is torsional stiffness while retaining the flexibiltiy of a soft flex of great benefit to faster swing speeds. Won't help my 92 mph driver swing speed but can't wait to see actual testing.
Happy Holidays to all,