The names do not make the jobs overlap
The standard Instant Pot Duo 6-quart is a multicooker with pressure cooking, slow cooking, saute, steaming, rice, yogurt and keep-warm functions. The Ninja AF101 is a 4-quart air fryer with air-fry, roast, reheat and dehydrate modes. The Duo in this comparison does not air fry; the AF101 does not pressure cook.
That makes this a comparison of useful jobs, not two replacements for the same machine. If dinner often means beans, broth or a wet braise, consider the Duo. If you mostly want to reheat a small batch or cook vegetables with dry heat, consider the Ninja. Both choices remain subject to the recipe and manual.
A six-quart pot is not six quarts of beans
The Duo's nominal capacity is the size of the pot, not the allowable cooking load for every food. Expanding or foaming ingredients require particular fill limits. Follow the manual and a reliable recipe, and choose the specified pressure-release method. Do not improvise a quick release for starchy or expanding foods.
The cooking timer also leaves out time spent coming up to pressure and releasing it. For a meal that must be served at a particular hour, include those stages in the schedule. A short programmed cycle does not prove a short total elapsed time.
An air-fryer basket has another limit
The AF101's 4-quart basket measures volume. Foods that need a single layer have a more practical limit: the flat space available at the bottom. A piled basket is not the same cooking arrangement as a shallow layer, and a large quantity may need several rounds.
Ninja lists a temperature range from 105 to 400 F and dishwasher-safe removable parts. Those details support the listed modes and cleaning routine; they do not establish how evenly a specific food browns.
Make room for the job you repeat
Shortlist the Duo if you want wet batch cooking and pressure-cooker functions. Shortlist the AF101 if you want a smaller dry-heat appliance for roasting and reheating. If you already have a good pot or oven that handles the task, keep using it until an actual inconvenience justifies another appliance.
For either purchase, check the counter space, outlet requirements and the clearances in the manual. Keep steam and hot exhaust away from hands and obstructed surfaces. Choose around the documented capacity, cooking modes, and the meals you want to make.
Keep in mind
Compare published product specifications, care instructions, and the features that matter for your cooking.
Pressure cooking requires the exact fill and release instructions for the food being cooked.
