The only "for sure" way to ensure that your horse is getting the joint care needed, is Intramuscular Injections like Adequan, Legend, Glucosamine etc, etc.
Talk to your vet.
I personally dislike oral suppliments because they fall under the "Equine Nutrition" category which isn't as strict in regulations as products that fall under the "Equine Medical" category.
Orals aren't 100% because of how loose the rules and regulations are in the Equine Nutrition category...so the "ingredients" may not be what they claim them to be, and the % of each may not be what they say there is.
Also, studdies show that all of the oral product that our horses injest, wont get to where it is needed. A small amount may get to the joint where the rest goes to waste.
Where Intramuscular Injetions and Joint Injections, fall under the "Equine Medical" category where the rules, laws and regulations are very strict. So, what the product says it is, it is and you can be sure that the product is going directly to the horses joint doing the job it is made to do. Products that fall under the Equine Medical field are strictly inspected, tested and proven to be effective.
Again, talk to your vet.