I think of how successful Char Broil was at marketing the Big Easy series of products as .."oil-less deep fryers", or some such thought...
And - they work....very well....but, "fry" is a term found lacking for most of us. And - like you Gordon, I was highly suspect of the "air fryers".....but - they have become a staple for a lot of folks. No, they will not cook enough of anything to feed a family of 6. At least ...not all at once. BUT...they do cook so fast that for many food items - it is still faster than 1 large "batch" cooked via traditional means.
I don't have an intellectually honest and objective opinion on any health "benefits" ...mostly because of the conflicting data even within the confines of the medical community...but this device appeals to many looking to reduce the use of fats to cook many food items. That + the time savings makes many a wallet fly out of pockets. High fat -low carb is very popular right now tho......And - even within the framework of that eating philosophy - the air fryer is popular because it allows more control over which kinds of fats and how much they are consuming.
I guess I see the air-fryers like I do the Instant Pot and Sous Vide. Just that. They are appliances. I will bet virtually everyone currently owns a microwave oven, and a Crock Pot. But, for the first couple of decades after their invention - many households resisted the microwave oven, either due to fear of "microwaves" or because they needed time to see how others re-developed recipes and methods to actually cook with a microwave oven. ( NOTE: tho we all own one - I will bet that few of us actually "cook" in them....but they are hard to beat for re-heating certain things...or making bacon, instant oatmeal, etc....
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So, like the microwave - but in an accelerated fashion due to the internet and faster, multi-phase media than in the 1970's
I I do believe that they will be shoulder to shoulder with the venerate Crock-Pot in virtually every home within 5-10 years.
Low cost to purchase , and speed/convenience are the 2 primary "economic food groups" for us as consumers. They are most often the reasons products either fail or succeed in a world driven by us as the consumers - for "faster and cheaper". You can thank the Personal Computer industry for re-programming us all to think this way......