The concrete mixer is good....for a few smaller calves.
Unless you have the $$$ for a proper mixer and doing a lot, it is easier to work out what the mob like and keep them so they will eat what your feeding, and just ad extras on top...
I mix lupin when doing smaller feed lots for younger calves, but after that, it is just sprinkled on to, or fed in a different feeding, seems you can always get them to eat what you want if it is controlled, but, yeah, it can take a lot of time too if they are not really hungry.
I can get them to eat most things, just watch, like anyone/thing, that you do not feed the candy at breakfast time :)