If you're a professional cook or even serious home cook, there are probably times when you want to bring some of your knives out with you—like if you're planning to cook with a friend and you want to use your favorite knife. Some of you may use a knife roll for carrying around a whole lot of knives, but if you're like me, you usually only need one or two knives. In those situations, blade guards make a lot of sense.
The magnetic blade guards ($9-$12) from Bisbell have a couple of advantages over plastic guards. First, they're easy to cut with scissors so you can shorten them to fit specific knives. Second, they hold the knives snugly, so the edge of the blade isn't bumping around the way it could inside a hard plastic guard. Maybe not a big deal if you're just taking your favorite knife to Aunt Susie's house to carve the turkey once a year, but it's more important if you use those guards to store knives in a drawer.
Although these things are magnetic on the inside, they don't stick to each other, so you can carry or store them together or with other metal items without worrying about them grabbing onto everything they touch.
While this isn't the most earthshaking gadget I've seen, I have to say it's a nice improvement over the slip-on plastic guards.
Disclaimer: Testing samples were provided to Serious Eats.