I’ve used this Harbor Freight air nibbler a few times to cut sheet metal for home and automotive repair, and it performed flawlessly. Let me warn you, though, it shaves off small quarter-moon pieces as it cuts, thousands of them — so make sure you use it in an open area where you can find them all, or in a place where they won’t cause problems.
The Harbor Freight air nibbler makes 3,180 strokes per minute — that’s where the thousands of small cut-offs come from. It’ll cut up to 16-gauge sheet steel, and combined with a straightedge it can give you a pretty straight line. The cutter runs at 90 PSI, but Harbor Freight didn’t quote a CFM usage; my 3 HP, 25-gallon compressor could keep up with it, if that helps you.
I was cutting some metal roofing for a chicken coop recently, and at first I tried my aviation snips, but it was just too thick so I switched over to the nibbler. It performed well, but it was very difficult to cut over the grooves or raised sections of the panel — still, the nibbler got it done.
I picked up this tool at the local Harbor Freight when it was on sale for $10 — like most air tools that come in at half the price of the “name brand” competition, I consider them disposable, but since I might only use an air nibbler a couple of times a year it’s no big deal to me. It normally sells for $25.