Ultimately what you’re trying to get at is your aerobic threshold.
In addition to @mcneese.chad comments about cycling, even in running using MAF is problematic. Best case it should just be used to confirm a rate of exertion you found another way. Otherwise I wouldn’t touch it.
I often approach endurance work with a power target with a heart rate cap. My cap by coincidence falls close to MAF so it makes for easy math while I’m exercising. But I use rate of respiration, RPE, prior experience, and ability to carry on a conversation to ultimately determine what it should be. Conveniently, it doesn’t change really at all (sure, over years, but…you know what I mean) so now I just know it. For you triathletes, it’s roughly your Ironman pace.
For those of you who might have done INCSYD testing, it is smack dab in the middle of your FatMax zone. For me, that’s 195W, or 68-69% FTP. I wouldn’t rely on using %FTP for it any more than using 180-age, but it will get you in the ballpark in order to validate/back up your subjective experience.
Another caution about using MAF is that you might actually be going too slow and creeping too much into Active Recovery. You’re not getting much endurance benefit out of that with the limited number of hours we all have to train. This is less of a concern for runners, likely for reasons @mcneese.chad points out. Hard to go too easy when running, VERY easy to go too easy when cycling.
For runners, MAF provides a poor man’s way of ensuring that you’re not overtraining, but honestly so does every modern coaching philosophy. You will go faster at the same low heart rate if you stick to it for a few months, but this isn’t a result of Maffetone method. It’s the result of common, widely accepted approach to running where volume is built primarily at lower intensities.