That looks a lot like a modern version of the Adel Tool Co. (Chicago) nibbler that I have that takes a 1/8-inch swath out of the metal. It is a bit big and takes a danged 1/2-inch hole to get it started in the middle of a piece of sheet metal.
For the square holes required by slide switches, I use one of two methods. One is to put the sheet metal over some hard wood such as oak and use a 1/4-inch or smaller wood chisel and a hammer to make the square hole. The other is to use a drill to start an undersized round hole and a Dremel rotary grinder to work out the bulk of it and small mill files to sharpen up the corners. That's why I like toggle switches with their round 1/4-inch or 15/32-inch holes. Trouble is, slide switches are so darned cheap and I have hundreds of them! Hate to waste the things.
Dean