I am posting this for my brother that is a looker not a poster. He is thinking about purchasing a vertical feed mixer for a dry lot Cow/calf operation of about 100 head  along with back grounding the calves. He will be mixing dry native hay, alfalfa silage bales and sorghum Sudan grass  Silage bales along with corn, distillers grain and minerals. He is wondering what he should look out  for when buying a used one. What are your thoughts of twin screw versus single screw wagons? what are some of the options that are a must have? 

He has just started looking so brands are pretty much of it in the air yet. Are there any that are definite stay away from mixtures?

Thank you  in advance

(edited tor wording)