Sure, you can scale a fish with the back of your knife blade. I did for years — until I drove my thumb into the dorsal spike of a striped bass. After having surgery, I picked up this little device at the tackle shop. It offers more than self-defense. It’s just absolutely good at what it does, and costs less than ten bucks. Show it to your friends and make them guess what it’s for; they’ll be stumped. What would make you design a fish scaler with what looks like plastic hex-head bits loosely attached to the underside of a circular disc? It doesn’t make sense. But it works! It defends your thumb (thank you) and prevents scales from scattering all over and flying up into your face. Only a little pressure is needed, and the fish is completely clean in seconds.