I started my horse on SmartFlex I last month, plus grand hoof, plus omega 3's. The smart hoof is only 20 or so a month, but of course if you add, shipping, it's closer to 30. That's why I went ahead and added the other 2 supplements, because then shipping is free.
So, I have NO idea, why, but my horse is quieter and calmer with this mix. Could be the omegas. Could be because his joints were bothering him and he feels better now. Also, a friend at the barn told me that unless you're getting Cosequin, you're wasting your money. But so many people are happy with smartpak I figured I'd do that, since it's so much cheaper.
My final bit of trivia is that due to other things, I started myself on a glucosamine and Chondroitin sulfate supplement last week. After only one week I feel so much better! I didn't even know I was stiff and achey all the time until it went away. So this stuff definitely works, if you get the right dosage (well, for me, anyway).
I would probably ask for a free sample from smart pak, since they are so good about that. I had tried some other cheap supplements from a local store that were powder, and my horse would not eat them. I have to have a supplement in pellet form.