Duct knives, including this one, are designed primarily for HVAC installers and other insulation installers. The two sides cut differently: plain side for clean cuts and can be sharpened, and the serrated side for quick cuts. So far I have used mine for cutting cardboard, rosin paper, rope, string, roots, branches, and plastic strapping and it has excelled at all of them. What Milwaukee does not say is that this is a great general-purpose knife that many tradesmen, contractors, workers, fishermen, campers, hobbyists, outdoorsmen, and weekend warriors will find useful for a variety of applications.
I do not want to call this knife disposable but for the price and its robust design you can certainly use it as your "beater" knife that gets used for everything from demolition to digging to landscaping to finish work. I would recommend a sharpening stone or smooth file to keep the plain edge sharp.
Highly recommended whether or not you use it for ductwork.