I use a whey protein that is 80% whey concentrate and 20% whey isolate. It tastes good and is not too expensive. So I go to a nutrition store to buy a casein powder, the guy says how much better this other blend is compared to the one I get from Costco. So I look at the package carefully and guess what, it's also 80/20. He has a 100% whey isolate that is outrageously expensive. Is there really that much of a difference?