I've bought a few of these for various people I know who live off the grid. Things to look for if you want to buy one:
If the shaft (or spindle?) for mounting the wheel is only 1/4", then it will take some cobbling to make it fit the smallest hole adapters (1/2") found in new grinding wheels...
The clearance between the shaft and the workbench will determine how large a wheel can be used. Having room for at least a 6" wheel will give many more options for wheel replacement, and a larger wheel gives a flatter surface with less of a hollow grind. I found one that accomodates an 8" wheel.
Some guys on woodworking forums use these to sharpen their chisels, since the low speeds won't heat the steel so much. They put the more expensive white wheels on these grinders, which grind cooler but wear faster (more friable). They also seem to unanimously recommend the adjustable tool rest/guide sold by Lee Valley, which will probably cost more than the grinder.
Here's a photo of somebody's setup, which shows the Lee Valley tool rest which can be adjusted to any angle for wheels up to 1" thick: