The advantage of the scraper style sharpeners are the ease of use and the preset angle. They require little or no training and experience.
They can only sharpen relatively soft steel and tend to break small parts from the edge. This creates a rougher edge. They also shave off more material than a stone. Of course the angle of the edge cant be varied. Hence the angle of an edge can´t be maintained. They are totally useless for serrated edges.
With a stone any sharpening angle can be maintained and the result is much smoother than with a scraper. If you sharpen the knife before it is really blunt the work is done with a few strokes. With a proper stone even serrated edge can be sharpened. I prefer the diamond "stones" over real stone. They can be dropped without breaking and they are available in pocket size.