yes! i had a guy come and he was fantastic. saved me a fortune in supplements and branded food that I didn't need. He simplified everything, my feed bill is about a tenth what it was, and the horses look great.
I used one recommended by a vet hospital when my mare was diagnosed with PSSM. As a starting point it was a really good exercise because I was feeling a bit lost at the time.
Yes, I have used an independent nutritionist for a horse with gut issues. It was worth it for me. She gave me a number of different feed options. There's so much marketing hype, it's difficult for the average person to know. Yes feed nutritionist have there uses as they are free, but I'd rather pay for independent personally.
I've never used one, but have often wondered about it
I have used a free trial of the FeedXL app once which once interesting. I prefer straights, but it was nice to check energy and protein levels.
I have a friend who trained as an equine nutritionist and is excellent at her job but she couldn't make ends meet and was working a second job to be able to cover the bills. Eventually she took a well paid full time job to be able to buy a house etc.
So yes, there is a demand but it's limited, particularly when you're competing with free advice from Equine nutritionists at feed companies. You might be able to make it work as an 'on the side job' to bring in some extra pocket money, but you'd struggle to make a good living from it.