Has anyone tried this?

[Mother of Chaos]

It's not cheaper.
It's not superior nutrition.

I can think of no rational reason for doing this.

I can only assume your mother saw this on some social media site, has not recently priced rabbit food, bird seed, or cat food, and has spared no time to critically thinking this thru.

Your gut is correct

Am I the only one who hears the word “influencer” and my brain turns it into “con man/woman”?

 

[BigBlueHen53]

If you offer your chickens bird seed or a mixed formula, I think there is a good chance they will pick out what they like and not get a balanced diet. A bit like putting jelly beans in mashed potatoes and hoping your two-year old will eat the potatoes. Yeah, good luck with that. Scientists have formulated a balanced diet for chickens. Feed them that and they'll do fine. These "influencers" are NOT nutritionists.