Depending on the size or type of art (or craft) works one is doing, carton or box cutters may or many not be on one’s radar or considered a useful tool. But even if one isn’t using them for opening supplies or actually during the art-making process, it still isn’t a bad idea to have one around since they’re cheap and easy to use. The dozen-for-five-dollars that these are priced at might be a bit larger set than most people would need, but it’s still inexpensive enough that it wouldn’t be hard to pick up.
Tap knives are one of the simplest types of box cutter. On this model, the outside sleeve is a single aluminum piece that has been bent around on itself. Inside is another piece of aluminum that has been folded with a cutout at one end and a flare at the other. A standard single-edge razor blade fits in the cutout end (and can be replace by sliding the insert out of the housing) while the flare prevents the knife from protruding too far forward.
Use is simple. Tapping the back of the knife against a hard surface will extend the blade until it is stopped by the protrusion on the back. And when the cutting is done, the front of the knife can be tapped on a hard surface to retract the blade. Very little of the blade is exposed making it fairly safe to cut with, and it’s held in securely enough that I wouldn’t worry too much about accidental deployment of the blade. How well it cuts and how long it lasts depends on the razor blade used. And the ones that come in the package are not the greatest. The points are especially brittle, and while they can keep an edge for a decent amount of time, they will crack and split with too much stress.
As far as a cheap, effective, and simple box cutter goes, they work well enough. The fit and finish leave something to be desired: the edges are rough, the tolerances vary quite a bit, and no surface is smoothed and finished, but they are so inexpensive they are practically disposable. They cut, they’re reasonably safe, and they could last quite a long time since there’s not much too them. One could get better quality, but I’m not convinced you’d really need to.