I have seen a drastic improvement in my Running times and Triathlon times. On my 3rd bottle.
I don't know if it works or not, but I seem to have more endurance when I am taking it. Even if it is all in my head if I feel stronger, I'll take it.
It is a bit pricey for a subjective perceived benefit.
Used for a couple of years after reading a positive review by a medical professional who was taking it himself. I cannot claim any better performance, but I do believe that my recovery time after intense or endurance events was much improved. Ultimately I stopped taking this as this expense is so high.