INSPIRATORY MUSCLE TRAINING (IMT) Opinions?

[tmr5555]

Going down the rabbit hole of marginal gains, I recently came across "Inspiratory muscle training".
http://www.cycle-speed.com/marginal_gains.htm Claims an incredible, eye roll inducing almost 9 minute improvment in a 90 km TT (such as the bike leg of a half ironman).
Some info on the subject: https://semiprocycling.com/imt
A litle more info: http://www.220triathlon.com/training/bi ... /4637.html

What do y'all think?
Trying to keep an open mind without being gulliable...