Believe me, I've done a lot of homework.
There are a lot of case studies that show how it's help individual horses. Dr. Beth Valentine has written about a few of them in her book. Granted there are people that believe it works and those that believe it doesn't. It's just like anything in the horse world.
Luckily our vet clinic is highly regarded and well versed on up and coming research. But you should always check with them anytime you want to make a change to your horses diet to make sure it's going to be the best. THEY know the particulars of your horses care and needs.
I've had a happy healthy horse for 10 years that he's been on it.