I used some to supplement bad hay one year. I don't care for it much though, as it has molasses. And the brand we were feeding was 100% alfalfa, which I don't care for either.
I currently feed just good Bermuda grass hay with Purina's FreeBalance mineral/vitamin supplement, no grain or pellets. They're doing great! I'm adding some black oil sunflower seeds (4 cups a day) to my Anglo Arabian's feed as he can drop weight in the winter. BOSS is very high in fat and has some great nutrients in it, and it won't hype them up like sweet feed and some pellets will.
I don't like feeding grain or pellets. Molasses, corn, wheat, and "sweepings" are just not good for horses. Recent research has found that a lot of horses are IR and even mildly laminitic (without the owner's realizing it) because of all of the rich high sugar and high starch feeds we give to them. Horses are built to eat GRASS, not sugar!