I use mine a lot with Class 5 that needs to be spread on one lane private roads. The consistency of the Class 5 is important. If the stuff is too wet or has too much binder, it can cause problems. This summer I was hauling from a pile in the pit I normally use with great results spreading. That pile ran out, so I moved to a new pile about 500' away. Went with the first load and raised the box like the previous load, very little came out so I raised some more and it plugged the tailgate. Started putting the box down and it decided to start coming out again. I called the owner of the pit and he tried some with his truck, ended up having to have the gate open one more chain link. He changed his mixture some and then it was good the rest of the summer.
It is great when it works right but you can make a mess if there is a problem. Spreading up and down hills can be a challenge too. You especially have to be careful going up a hill with a lot of dirt in the back and box up high.
FWD