I have been on a quest to find sturdy, tough chew toys for my jack russell terrier. She normally destroys toys and chewies within minutes, but these hooves really last. The only drawback is that they smell sort of bad -- and the odor grows as she chews on them. But, they successfully keep her happy and occupied, so its worth putting up with the smell.
I bought these for my rat terrier, who cannot eat rawhide chews because they upset his digestion. He spends many hours chewing away, and I haven't seen any negative side-effects.