I have owned an oven, toaster, toaster oven, air fryer, dehydrator, deep fryer, microwave oven. Air fryers use a fan to circulate the heat. While a toaster/convection oven typically use radiant heat. Upside to air fryer is the speed. Downside is it will tend to cause fats to render out quickly making the food more on the dry side. Some foods/diets are suited to that style of cooking.
Growing up my parents almost exclusively used a pot shaped one with the fan/heater in the lid, to make roast chickens. The skin usually came out nice and crunchy and spicy. It would be tougher to get that same effect in a toaster oven or oven. They also tend to heat more evenly so for reheating they cook better than a microwave. But can not beat a microwave on speed.
Think of each of these as tool to get things done. Each one can mostly do what the others can. But some tools are better suited to cooking styles than others.
Growing up my parents almost exclusively used a pot shaped one with the fan/heater in the lid, to make roast chickens. The skin usually came out nice and crunchy and spicy. It would be tougher to get that same effect in a toaster oven or oven. They also tend to heat more evenly so for reheating they cook better than a microwave. But can not beat a microwave on speed.
Think of each of these as tool to get things done. Each one can mostly do what the others can. But some tools are better suited to cooking styles than others.