I have one of the teagle spiromix units. It is designed like a large truck mounted mixer in which it has a spiral paddle in the drum and dumping is achieved by mechanically reversing the drum rotation by pulling a rope connected to a lever which switches a gear on the pto. It works pretty good and will dump into a wheelbarrow. My only complaint about the unit is it won't mix a stiff batch as it really tends to stick and won't unload, it needs to be fairly wet. It will mix about 15 shovels worth of gravel and whatever ratio of cement you'd want. I find too it helps to load most of the water first, then gravel, and cement last or else some gets stuck in the back side of the bottom of the spiral.