Hi there!
I fermented for 2 years... so I will give you my take.
I will start by saying that I feed 20% protein flock raiser to ALL of my birds from start to finish. And all the labels like layer, meat bird, finisher, grower, starter... are all confusing terms and each company makes up their own name... MAIN (not only) difference is protein and calcium.
First I saw almost NO savings... people who do see the
most saving are those who this diminished waste for.
Some feeds already have probiotics added in... and you could add some by using raw acv in your water. And to me... you don't get something for nothing. While some nutrients will rise slightly, others will decrease... and formulated rations... are FORMULATED to meet the need of the birds.
Check out this article of you haven't seen it...
https://tikktok.wordpress.com/2014/04/13/fermented-feed-faq/
It claims to increase protein by
"12%"... but that can be a bit confusing of a statement... noting it doesn't make 20% protein into 32%... but rather this is how I figure it... 0.20 X 0.12= 0.224 or 22.4% protein... So their is SOME increase... however... none of the studies focus on what is now decreased that I have seen. One person actually sited a study that had two sets of birds one raised on FF and the other dry... The FF birds were lighter for a period of time in the beginning but eventually caught up to the dry fed birds... I WISH I could find that post again and I feel like it was about 8 weeks... BUT the memory is a feeble thing.

Either way... I'm wondering if this "conversion" alters the caloric content... but feel as though it must alter something... if you don't FEED the ferment with fresh stuff... the bacteria runs out of stuff to digest... so is it using calories or turning itself into calories or what?!
Anyways... after doing ONLY for 2 years... it did NOT save me the 30% many claim... maybe not even 10%... but I spent TOO much time and energy doing it for a very large flock, think 30 gallon trash can.. I quit for the longest time as decided it was MOSTLY hype... now I offer FF as a breakfast and they seem to enjoy it.
One thing is... it will be especially beneficial for flocks who may be struggling... But like with vitamins or other supplements.. will do very little for those who already have nicely balanced immune systems. In MY experience.
I always appreciate a logical and intelligent conversation and love to see what others are thinking!