If you do not remove enough metal to create a new edge, you will leave some of the dull edge in place. The easiest way to determine that you have removed enough metal is to grind until you have raised a burr. Steel will naturally form a burr when one bevel is ground until it meets another. You can then remove the burr in the honing process and have a sharp edge every time. A final honing and polishing will bring the edge to perfection.
Diamond stones are the fastest cutting manual stones, with Japanese waterstones second.
The first step is where most of the work is, and you can benefit most from using a power sharpener. Set the guide and take a light stroke with the stone. Check the angle against the old bevel. If the new scratch pattern is on the back edge of the old bevel, you are lowering the angle. If it is at the edge, the angle is being increased.