I got one of these as a gift eons ago and they actually work quite well! Having to replace mine as it was taken to sharpen my dad's lawnmower and never brought back! ...thought this was a good price.
* Sharpens any knife with diamond precision
* Sharpens hardened knives (e.g. Global, Sabatier)
* Even sharpens serrated knives (e.g. bread knives, hunting knives)
* Very safe one handed use, PowerGrip suction attaches securely to any flat surface
* Dimensions: 60mm diameter and 60mm high
Some good pictures, tonnes of reviews & a Barry Scott/Alan Partridge style demo video in the 'go to deal' link.