I don't believe there's any really scientific way to measure the results of the various supplements. They claim to do many different things, all of them very subjective in nature. Rate of gain can be measured, of course, but you can't really say how much difference the supplement makes between different individuals, as their gains would most likely vary from one another anyway. Things like hair quality, soundness, appetite, freshness, or bloom can't be measured. I think the best you can hope for is to listen to others' experiences and recommendations, if you're lucky maybe you can watch what your friends and neighbors use and draw your own conclusions, but ultimately you're gonna have to try them for yourself. What seems to work best for me, and/or what I think is worth the money, may not work as well in your situation, or you may not feel the results justify the cost.
My opinion? We're feeding Shag.