I've got a friend who swears by this stuff for her horse. I don't think she uses it for "hindgut management" but does consider it vital for keeping weight on her horse, and other probiotics have not performed as well.
I have been at two barns where Forco was used exclusively, and it didn't work at either barn. Not quite sure why they kept buying it? If you're looking for something that will actually work, try AssureGuard by Arenus. Helped my mare out so much, her attitude changed noticeably. Not as cheap as Forco, but in my experience, much more effective.
However, I think some people on this board have had great success with it. Research both products and ask your vet for a recommendation, he/she will know what is best for your horse.
Forco contains Saccharomyces cerevisiae, which is plain brewer's yeast.
Saccharomyces boulardii is the strain that has show some ability to help the hind gut heal. It is more expensive, and not in the list of Forco's ingredients.
Research the two strains of yeast and then you can make an informed decision.