I have never used one but have heard they are very heavy and slow if used for cutting hay bales. My tub grinder man has had a couple of customers that got them and now have gone back to tub grinding. Good Idea but still need 2 tractors and takes longer to feed.
I've got a supreme, and I think any vertical mixer is going to do a good job. The moving parts are way fewer than any horizontal I have ever seen.
I grind the hay with mine too, so a horizontal wasn't even really considered.
Some drawbacks, they are heavy, high (takes a big machine to reach to load). The recutter attachment (bale shredder) is not a good investment, it takes way too much HP. A seperate bale processor would be better.
Like every machine, you'll always wish you had the bigger one sometimes.
They mix very well, extra time in the machine doesn't allow fines to work down.