I have a Stihl USG. I also have a Maxx grinder. The HOS has a fixed head whereas the USG allows you to adjust the head. I just received the USG so I haven't assembled it yet. I can tell you this about it though. It does not come with a light whereas the Maxx has a built in light. The USG spindle is 12mm (1/2 in) whereas the Maxx and others use a 7/8 in spindle. The grinding wheels on the USG seem coarse and are slightly smaller in outside diameter. Overall the USG is a well built quality machine. If you are going to sharpen mostly Stihl chains and are a perfectionist, the USG corresponds directly to the angle recommendations on the chart that comes with it for Stihl chains. I am not sure you can achieve all of these angles with the other grinders. I have CBN wheels for my Maxx grinder and have ordered a ABN wheel for my USG grinder from Edge and Engine. They have an ABN wheel with the 12mm spindle. The CBN wheels do an excellant job on my Maxx grinder. The nice feature of the Maxx grinder is that it clamps the chain automatically when you bring the head down. Also the head can be positioned left to right allowing you to reverse the chain in the vise and grind at the same position for left and right cutters. I like the Maxx grinder and have found nothing bad about it. A couple more things about the USG grinder. You can get accessories for it that allow you to grind hedge clippers and rotary saw blades. You can also get a light attachment and an foot petal attachment to clamp the vise as you grind. Of course these accessories drive up the already high purchase price.