I bought a small wheel barrow mixer from Home Depot a couple of years ago for about the same money, $350 to $450 IIRC. I prefer this to the 3PH model as it is easier to get into tight spaces and is perfect for dumping into postholes. I have used it quite abit with no problems so far. When I am installing lots of posts I use my backhoe with pallet of concrete on the front and hyd auger on the hoe, followed by a small cart with water buckets and Honda 2000 genset for the mixer. This reduces the amount of labor dramatically for me. Most jobs around the house or construction sites a plug in mixer is way less trouble to use.
Really enjoyed looking at your guitars on the site the other day, wish I still had my old NY Epiphone.