I have a similar tool called a 'Speedy Sharp' - I think it was about $5. I like it for hasty sharpening at the expense of removing what I'd consider 'too much' metal. Much more than a conventional stone (and hence, much faster). I would never touch a precision edge, such as a plane iron with one.

I have a drawer-full of sharpening gizmos, but after many years I'm convinced that there's really no substitute for stones - although there are poor to great stones. They all require some understanding of developing an edge, particularly if a fine edge is wanted. Probably the easiest (for knives) is the Spyderco Sharpmaker. Probably the best is anything that helps you hold an angle, high quality, flat, stones, and developing a little skill.