This just came through the post today.
It is a buttonhole cutter; the ones that are used by proper tailors.
There are several types that I’ve seen on the internet. They are mostly the ‘chisel and woodblock’ ones that only cut a straight hole for bar buttonholes. Another type has a handled hole puncher included for the keyhole. The pilers type are few and rare and cut straight holes but this one can cut the keyhole and slit at the same time.
There is an aluminium pad with inch markings on it that you can adjust for the right length of buttonhole (it can cut a hole from 7/8″ to 1 5/8″, with or without the keyhole). I managed to get another of these pads made bespoke so it would allow me to cut buttonholes 3/4″ long so it would be suitable for small cuff sized buttons (22-23L).
Very useful and it works well. Made in Italy and is vintage. I am lucky to have won it off eBay for around £18.