The link you entered isn't working, however, a thought here. First, not all supplements work with all horses..which is why there are so many out there. If you do an ingredient comparison on any similar supplements, the ingredient list may read very similar but the amounts may be slightly different. While one horse may have good luck with a certain portion of this or that ingredient, another horse may have no reaction at all. The ingredients for the coat and hoof are essentially the same so if you aren't seeing improvement in the feet, which you said were good anyway, it is because the feet are getting the nutrients for health they already need or because they are/were in such good condition anyway, you just don't notice any changes.
Given the description of your horse and his improvement, I would say that if the supplement for which you provided the link is the supplement you are using then that supplement is the "best" for your horse regardless of reviews.