Why is Mountainous/Hilly Gran Fondo Program :
"BEST FOR
** Riders who have NOT taken the Full Frontal fitness test in The Sufferfest app OR for those who wish to base their training on RPE / FTP-based metrics*
"
I cannot understand why this plan is better for riders having not done the FF ?
Any explanation ?
Actually, this remark is only added when you select the plan option with strength. It vanishes in the normal “indoor+outdoor” option.
I don’t have the definitive answer for you, but looking at the scheduled workouts, a lot of them are done outdoors, where your 4DP numbers won’t matter or are done indoors on technical videos, again, where your 4DP numbers won’t matter as much.
My thought is that most of the “key workouts” are outside of the 4DP metrics and done by RPE anyway. So in my opinion, this note doesn’t seem to be so far off the truth. 
I hope one of the coaches can give you a better answer than me.
@Pierre Thank you for your reply. I think it seems to be more a mistake than anything else. Your remark regarding the fact that the mention is only present with the strength added reinforces my idea (I didn’t check before). I do not agree that the 4DP doesn’t matter for outdoor riding. Regards
Could be a mistake. I still doubt it. 
Let’s hope somebody clarifies…
In what way do you think your NM, AC and MAP numbers come into play?
According to this description of SUF outdoor workouts, only RPE and FTP are needed as a guide.
Of course, you are right that knowing your numbers can lead to a „better“/„more guided“ workout outdoors, sure.
Certainly looks like a mistake in the description. Also makes little sense as the plan is tailored to your rider type and has 4DP adjustments. There were non-4DP versions of the plans, could be a hang over from that.