My $0.02 of opinion: If as you say it's efficiency you're after, go electric. Since time is an element of efficiency, an electric belt sander or grinder will remove metal in less time than other methods or systems. Which motorized system you choose is up to your personal & financial preferences.
My experience: Using a 1x42 belt sander with 60 grit belts saves me a *ton* of time when friends or family want me to sharpen a knife that's about as sharp as a brick. It allows me to thin primary bevels, set secondary bevels, & establish edge apex to a burr very quickly, before a brief session on diamond sharpening plates/rods and a strop knock the burr off & refine the final edge. 1x42 is long enough that the blade never gets more than slightly warm, if you use a light touch & monitor temp with your finger tips as you're grinding. FWIW, I grind edge trailing 99% of the time and grind with the belt going into the edge *only* when I need to reestablish or refine a blade tip. And then I'm operating with EXTREME caution & only letting the belt barely kiss the edge. We're talking a touch lighter than a baby's sigh.