good for cheap knives

I take the knife sharpener only for "cheap" knife without serrated blade.
For my twin knife I only accept the sharpening steel, which extends normal always (so years until the end of life of the knife).
Grindstones or knife sharpener you need normally only when the cutter (below where the blade is sharpened) is damaged.
The knife sharpener gives the cutting a new sanding, minor damages (small outbreaks) you can grind away with many grinding passes (10-20 times rough side).

The blade sharpener is very good.

One should never been a knife sharpener for expensive blades take (even if it's on the twin home is!)

The cutting edge of good knives is Gemini also believe more easily U-shaped rather than V-shaped believe how many.
However, the knife sharpener makes rather a V cut.
In order not to change the various ground surfaces which may have knives, so V-, U- or V-shape, you should always use a sharpening rod, or grind at V and wedge-grind with a grindstone.