I know this is a really, really old thread but I felt I had to comment. I came across the thread while looking to get another of these.
It's a fantastic bit of kit if you use it in the way it's meant to be used (or maybe I mean how I reckon it's meant to be used).
It rips metal off things, and it's very good at that - and it leaves a very rough edge. You could sharpen an axe with it (and I have done). You can use it to change the angle on the edge of a knife. You can use it to sharpen a knife that hasn't been sharpened in years that you've been asked to sharpen.
Then you need to put a proper edge on the blade. I actually have one of these things on my keyring as well as a DC3 (yep, it's a very bulky keyring but I don't lose it very often) and I reckon I can sharpen pretty much anything with those two bits of kit - to a state where you can push-cut A4 if that's what you want to do.
It's not for getting a polished edge on a well-loved expensive knife, it's for getting an angle on something that's been neglected. And for that, it's perfect.
Cheers!