I thought I'd address a couple issues that were brought up the cutting angles for the two wheels are 18° and 22°
To address the issue of heat created while sharpening the knife is nonexistent. There was no heat that could be felled on the blade itself. After all, you only do two passes or a total of four per wheel and that's if you're putting a whole new edge on the blade. If you're just sharpening the knife you only use the fine grinding wheel. And the stroping wheel.
shepherded addressed the issue of taking off too much material. The coarse grinding wheel will definitely take off material. If you're stupid enough to hold it there. It will probably cut the blade in half. First you have to know how to use the machine, which isn't hard if you read the instructions, which is very short. When you drop the blade on the wheel you start pulling immediately.
I've used the chefs 130 sharpening machine with diamond grinding wheels so in comparing this wearing knife sharpener with stone grinding wheels. I believe the wearing knife sharpener to be superior. if anyone has used our has a chefs 130 sharpening machine. They will take off material but not near as fast as this machine. I would have to make a half dozen passes on the chefs 130 compared to two passes on the wearing machine.
To put the finishing edge on my knives I use this.
http://www.knivesplus.com/eze-lap-sharpener-ez-g.html
when I fish commercially, we had to have sharp knives and I've been sharpening knives the stones so much so that I have thrown one or two stones out and my other stones smiles at you if you look at it from the side almost a dog bone look. As far as a sharpening expensive knives especially knives. I agree with buzz do them by hand but for your everyday knife and this machine works fine, and you can do a dozen knives in no time. With that said in there is a place in for these types of knife sharpeners.in my opinion.