I was thinking about buying this handheld knife sharpener. You put the blade of the knife in the device and simply pull it through to sharpen it.  Is a device like this useful, or should I just stick with having my knives professionally sharpened?

You ask as if getting your knives professionally maintained is all that’s required to keep them sharp. Unless you’re getting this done often (commercial kitchens have it done weekly or bi-weekly), even in a home kitchen, your knives are getting awfully dull between sharpenings. So you need to be doing something at home.

Here are two questions you may not know the answers to. How hard is the steel your knives made of, and what angle is the factory edge? A knife made of harder steel will take a keener edge, but it’s more difficult to sharpen at home. Generally speaking, European manufacturers like Wusthof, Henckel, and Sabatier make their knives of softer steel than Japanese knives so they’re easier to sharpen yourself. On the other hand, the harder steel Japanese knives come sharper new and stay sharp longer.

With regard to angle edge, the majority of kitchen knives have an edge between anywhere from 20 to 25 degrees per side. This relatively wide angle will allow the edge to resist damage, thus lasting longer; but because it’s blunter, it’s not going to be as sharp as a knife with a narrower-angled edge. My Japanese MAC knives have a 15 degree edge per side. As a result, they’re sharper to begin with.

I don’t know which hand-held sharpener you’re referring to, and there are a lot of them out there. Some are set to a predetermined angle, while others aren’t. The sharpening material can be diamond (hardest), tungsten carbide, ceramic, or steel. A hand-held sharpener which Cooks Illustrated has been recommending for years is the AccuSharp. It retails for about $10. I don’t think it’s the one you’re asking about, because how it’s used is different – it must be drawn over the exposed edge of the knife rather than pulling the blade through a slot. It’s an option, though.

The Fiskars RollSharp, which MAC recommends, has a slot you draw the knife blade through, which puts it in the category you mention. I recommend this one as easy to use and inexpensive (about $15.) If you have both Asian and western knives, I suggest you buy two*. This/these will keep your knives sharp between professional sharpenings, which you really can’t avoid. Eventually a knife will become too dull to sharpen at home, unless you’re willing to invest in the proper tools and learn the technique. Mine go out every three to six months, depending on how much they’re being used. Yours may not need to go out as often.

Knives dull through use. Of course, they also dull through abuse – left soaking, going through the dishwasher, being jostled in a drawer rather than stored properly, used for tasks outside the kitchen… surely you’re not guilty of any of these things, I’m just saying… they won’t need sharpening as often if they’re treated properly.

* I discovered recently that the Fiskars RollSharp should be reserved just for your MACs. If you use it for both MACs and other manufacturers’ knives, the angle will become wider and therefore unsuitable for the MACs. So if you have a mix of knives, as I do, you’ll want more than one sharpener.