I like the Hydra-Bed caker, model 1800# (but it actually holds only 1500# of cake). It has a digital read-out mounted above the steering wheel, and it can be calibrated however you want it. We have ours set so that for every number on the read-out, 2 pounds of cake has been fed. In other words, if there are 150 cows in a bunch, we pull in and feed out to where the read-out says "150". That means that 300 pounds of cake, or 2 pounds per head, has been fed.
It is auger-style and hydraulic driven, and seems consistent no matter how much cake is in the hopper. An older one that I had several years ago, fed more out if the hopper was full than if it was half-full. The new one works much better.