There is merit to taking protein mid-ride but it's more in the BIG rides, 6h+, 4500kJ+ etc. so that the body doesn't use up muscle protein. I often bring a small bag of whey and drink it when I top up my bottles after 3-4h, or then I just buy a small protein bar with 20g protein for like 1.5e. Don't know why you would put it in the drink mix itself though