My favorite thing for making straight cuts in sheet metal is a metal cutting blade in a skillsaw. Not an abrasive disc, but a toothed, metal-cutting blade. Works great.
I had the Harbor Freight unit, and it worked just fine. Eventually, I sold it on Craigslist because I just didn't use it enough to justify the space it took up (My garage is really full).
Howdy. I am a 65 year old retired guy. Am into cars and trucks. Sold a Lionel train collection to buy my latest toy - A '55 Pontiac 2-door with a BBC under the hood. Also have a '27 T roadster with a 350/350 combo. Daily driver is an '07 Dodge Ram shorty with a 6-speed manual trans.