Those feeders look great. Do they just drop a pre programmed amount to feed all your cows at the same time or is it microchip activated when a cow puts its head in? We use NLIS tags over here (which contain a chip) and most feed systems in dairies and feedlots run off these.
What else is in your feed apart from protein meal? And what type of protein is it? (canola/lupin/soy etc)
I am of the opinion that cows do their best on grass,from a rumen health point of view, but working in dairy, we do use very high (6-15kg....13-35lb I think) of predominantly wheat based ration. It is unarguable that in finishing animals a little ration goes a long way and I am a big fan of biproduct rations (we use grape marc/brewers grain/olive pomace/citrus pulp etc) but they are only really being used experimentally over here at present. I also love kelp and molasses as a substitute for more traditional mineral rations. All my own beefies have done brilliantly on those two and they have the additional bonus of stimulating appetite.
let me know how you go with the feeder!