I've tried it on and off over the last few years. It's not a programme for those who like to get thrills from their workouts.
Some fans of the method are very quick to denounce the 220-age method of determining MHR, only to then swear by the 180-age Max Aerobic Limit - which seems pretty selective to me.
It's a very broad brush - but there are some pretty significant success stories out there, from athletes who've literally turned their careers around using it. It seems very well suited to athletes who have broken themselves with years of chronic over-training - it's very good at resetting your aerobic base; that is, if you have the time and patience to follow it.
My MAF rate is 121. This seems crazy to me - my RHR is 55, and my most recently measured max is 190. I can barely get on a bike and pedal AT ALL for 121.
And yet, I've been able to measure some progression when following the method - in that I've gradually developed more power for the same HR.
It's a long term method, that is utterly, completely and mind-numbingly dull, but if one has the dedication to follow it through, it can work.