I got myself a bigger bench shear a while back. This is a compound-lever shear.
It allows the user to cut much thicker gauge sheet metal than one would be capable of doing with a simple shear of any size.
Such compound-lever shears were sold as hand held ones that were about the size of a regular pair of tin snips, but provided a lot more leverage.

This thing is super cool.

When I first bought it, the thing had a few chips in the cutting blades, so I went ahead and sharpened them so I could use the thing, but at the same time I knew I was going to have to remove a lot of material, so the front of the shear doesn't close all the way due to that.
Not a problem, it works just fine as is.