I agree thoroughly! My horse wouldnt eat any of the others! And unlike most NAF stuff you only use a little bit so it lasts ages, and it has pre and pro bioic in it. After mystery illlnesses vet told me to put big boy on it for rest of his days!
Just put my horse on the Pink Powder because her poos are often loose, they've been fine since shes been on it and the tub is lasting really well. No side effects at all.
I use Protexin which I get from my vets. All my horses eat it quite happily. I think it is about £40 for a 1k tub, but it lasts ages, more than a month for 1 horse.
I use the pink powder ongoing as routine, but started with 2 measures in each feed and after 2 weeks went down to 1, and stick with that. I buy the big tub and dont have to replace it very often - maybe once every 3 months. No side effects other than better poops!