I don't think I would have the guts to look at the spinning blade and still consider putting it on my neck. I think stabbing with the knife is a quick method that's why some people did it, I think it would take at least a few seconds to get to correct arteries with a hand saw and cut them. I imagine it would be hard to control it because of the pain and also most people probably would abort the attempt after making a shallow cut because of SI.
As of effectiveness I think you would need to be under influence of a substance that would get rid of SI but wouldn't make your vision blurry or make your hands shaky so I guess alcohol wouldn't cut it.
Also the electric blade must be an expensive one, with a short blade, that is waterproof. If it gets fucked in the middle of the attempt it would suck ass. Honestly nothing else comes to my mind. Maybe butchers use electric blades? No idea