Electric sharpeners use rotating ceramic or abrasive-impregnated metal wheels to grind a new edge into a blade. Low-end models, which start at about $25, feature a single set of coarse wheels that produce a rough, if potentially serviceable, edge—it depends on how even the edge is, and that’s a matter of overall design and engineering. Higher-end models can cost $200 or more (and professional models for slaughterhouses can approach $1,000), but they feature stronger motors and multiple grinding wheels—coarse, fine, and often polishing/honing—that when well-engineered can put an extremely keen, durable edge on knives of every style and quality.

One of the most important factors in determining which sharpener is best for you is the type of knives you’ll be sharpening. There is a difference between styles of knives that will help you understand what to look for in a knife sharpener. To have a better understanding, see this guide on the differences between Euro/American and Asian knife blades.
As Mal Knives shows in a review, the Chef's Choice sharpener creates a triple bevel on the blade, which allows it to work with both Asian and European/American knives. The bevels are at roughly 25 degrees, 20 degrees, and 15 degrees. This triple bevel design increases the length of time required between sharpenings. However, one Amazon customer reviewer disliked the sharpening results on Asian knives with this machine.
There are consumers that used the Chosera stones for years with amazing results. Some even bought the different lines of Chosera stones since it can be hard to choose a favorite (just like the Naniwa Chosera 800 Grit Stone which is also highly recommended) and all serves different sharpening purposes. But many agreed that the Chosera 1,000-Grit is an excellent stone to create a new bevel on straight edge razors.

I bought this knife sharpener for my son as a Christmas present years ago and recently (but cautiously) used it on my cutlery (Henkel and Wusthof). Frankly, I had been a little lazy and let my knifes lose a bit of their edge. I did not feel like getting out my stones and oil to do a proper job, so I borrowed my son's sharpener. It really works great, which I hate to admit, as it feels like a cheat and it is a fraction of what I spent on stones. I realize that I need to buy one for myself, so I looked around to see if there is anything better and I could not see anything that looked better. This one is adjustable, which is what I need. I looked at the 1 star ratings and there was a common theme that the knife edge chatters as the blade is pulled across. It can, if you don't use it properly! If your blade is very dull, you will need to pull with a very light, steady, and quick motion. You never need to push down hard as you pull. Even pressure. Don't be a brute! Finesse is what is needed. I am going to buy another one for me.
"Sharpening is like a hangover cure," says Laurie Timpson, founder of Savernake Knives in Wiltshire. "If there was a cure and you knew about it, I'd stay at your house, crash on your sofa and have whatever it was when I woke up. Everyone would have it and there'd be no discussion. Everybody says they've created a perfect sharpening technique, and they haven't." 
Generally speaking, this type of knife sharpener is designed for someone with a little bit of experience in the craft of knife sharpening. To sharpen your blade, simply swipe it along the rough, textured surface in a sweeping motion, being sure to hold it at the proper angle. Holding it at the proper angle can be quite difficult. Despite looking very basic and simple, this is actually one of the more difficult types of manual knife sharpeners to use. That being said, with a little practice almost anyone can learn how to use it effectively.

My husband bought this to sharpen my cooking knives which were extremely dull. Now this didn't sharpen certain knives that we have but the ones I use all the time including my meat cleaver are now razor sharp. It is worth the money if you or you know someone who knows how to use this product. Remember that knives have different types of blades and some will need to be professionally sharpened.
This set of two Norton combination waterstones provides four grits and also includes a flattening stone as an added value. The 220, 1000, 4000 and 8000 grit sides will handle everything from aggressive shaping to final polishing. They are 8" long by 3" wide, big enough to handle most knives and tools easily. Our most popular waterstone kit, this has everything you need to both sharpen with waterstones and maintain the stones themselves. A great starter set.