Well been playing today and have two options open to me, Air Nibbler & Air Shear. I found the Shear is great for cutting fast straight lines and the nibbler is better for cutting curves. So far glad I have not spent £££ as I can now use both.
I inherited an electric shear from my dad; it's an ancient thing, all-metal construction and called a Lesto GEG-1 made by Scintilla SA.
I Googled it and turned up a magazine article about it from the 50s!
Goes through sheet tin like the proverbial hot knife in butter.