Like Russ, I have both a Square Wheel and a KMG. I purchased my
Square Wheel from Koval knives many years ago...in fact at the time, I paid a total of $585.00 which included the shipping. Its been a very reliable machine. The drawbacks are availability of parts, and if you purchase the single speed version, its WAY too fast. Before they were ever available, I had a slow down pulley custom made for mine, which made it a much better knife making machine. I've gone through several sets of the various bearings, and 3-4 toggle switches, but its still doing its job after over 25 years of use.
If your looking to purchase your first grinder, I would have to choose the KMG. It's a machine made for knifemaking, and in my opinion much better built that the Square Wheel grinders of modern day.