The Ninja Foodi is larger and takes up more counter space because of the attached air fryer lid. The Instant Pot Duo is more compact and might be better if space is your primary concern. However, the Foodi combines pressure cooking and air frying in one appliance, which could simplify your cooking process overall. If you air fry often, the Foodi might be worth the extra space. If air frying is occasional, the Instant Pot Duo plus a separate, smaller air fryer could be a more space-efficient solution.