Every year or so a new wiz bang sharpening system for chisels and planes comes on the market. Below are four criteria for evaluating whether a sharpening system will work or not.
By grinding I mean the course operation of establishing the basic shape of the bevel. By honing I mean using fine abrasives to make the back and bevel of the tool meet at a perfect line.
Requirement #1. Grinding
Any system you use must have a way to establish the primary bevel. This is a course operation that requires a lot of metal removal. Even if you buy new tools and never mess up sharpening, you will need to grind. If you buy old tools, you will definitely need to grind. The accuracy of the grind required depends on the overall system you choose.
Requirement #2. Repeatable bevel angle in honing
For any method of honing, you must have a repeatable method for registering the blade with the abrasive to form the bevel angle. Accuracy is nice, but not required in setting the bevel angle. If the setting is not accurate, you can usually make it a little steeper and things will work out fine. However, if it is not repeatable, then you end up removing a lot of metal, which makes sharpening cumbersome.
Requirement #3. Repeatable method for lateral adjustment
Like setting the bevel angle, making the edge square to the side of the blade does not have to be accurate, but must be repeatable. (There are a few exceptions to this, such as mortise chisels and shoulder plane blades, but in general, edges that are slightly out of square function acceptably.) If the registration is not repeatable, then every time you come back to hone, you end up removing a lot more metal from one side of the blade than the other.
Requirement #4. Method for correcting registration errors in lateral adjustment
No matter how accurate or repeatable your lateral registration method is, you will need a way to correct for errors in registration. If you don’t have a way to correct for registration errors, then you will end up removing a lot of metal from one side of the bevel with fine abrasives, which takes a long time.