I haven't tried one yet. Most of our hay is grass and I've been told that those mixers and grass hay aren't a good match. If you are putting silage bales and alfalfa through it you shouldn't have a problem.
Well, for what it's worth, a friend of mine was a dealer for these mixers and demoed one at a rendering plant. They "processed" 6 Holstein cows and a Clydesdale horse through one. Said it did ok if you could get past the sound, but the hides tended to wrap around the vertical screw. Takes a special kinda person to do that I suppose.....................
Aside from the functionality of the mixer, those animals were dead, weren't they. Think what we would miss out on if animals were simply given a burial. None of those 'other' things we get from cows.......from ingredients for a multitude of items ranging from nail polish to vehicle tires. The list is long, and beneficial products makes more sense than creating a disposal problem when a cow or horse dies.
The worst job in what you described would be the clean-up! The guys here grumble about cleaning out the twine.....that's nothing in comparison to the hides! Guessing the cleaning crew was thankful it was not their every day job.
I have a used Twin Auger we have run for about 10 years. Need to have a Sleeve kit put in. We have mixed a variety of hay and wet processors waste during that time. I would say most issues were operator error in that time. Overall, pretty happy with it. But, I haven't used anything else to compare