Sometimes marketing departments come close to telling the truth, and for once the hype printed on the side "The worlds best knife sharpener" is not far from reality. This little gadget does actually work really well, and is very easy to use.
I bought this to replace my aging rotary hand sharpener that had seen better days. The steels on the inside were beginning to rust, and the results were not that impressive. As a passionate amateur chef, a decent sharp knife is essential, I realised my aging chefs was past it's best as well and debated buying a new one. I'm glad I didn't, as the AnySharp brought it back to life, despite the multiple nicks and imperfections on the blade.
As others have mentioned, this will take quite a lot of metal off the blade, but the results were impressive. Slicing through onions was a breeze, and I could cut transparent slivers of onion without effort. I tested the sharpness of the blade against a sheet of A4 paper, and while nowhere as lethal as some of the Japanese knives costing a small fortune, it cut through the paper with relative ease.
I'm not sure if this will last 20 years like my other sharpener, or if it will damage the surface of the knife over the long term. Hence the 4 stars. Not having whetstone skills, I don't know how much material a stone would take off in comparison. If you are looking for something that will sharpen a knife blade with ease and bring it back to life, it is well worth the money.