There isn't a spin feeder made that will throw enough protein to make any nutritional difference unless there is only one or two deer eating it routinely.
That may be, I am not thinking it is going to create some huge increase in mass. But I will say that more bucks come into this feeder than feeding only corn. Also, from a moral standpoint, I just dont see the point of feeding corn that has little to 0 nutritional value to deer. I at least am helping them a little.
I also do have a couple deer that are always coming to my feeders, one of them is a buck 10 point buck that was broken off during the season and was blinded in one of his eyes (presumably by fighting) he is still alive as of last week and sometimes sleeps next to the feeder.
I just try to help them out where I can.