I think it saves a fair bit. You're comparing it to a grill, rather than an oven, which probably averages 2kW, and has a 10-15 minute warm-up time during which it's probably 4kW.
We have a halogen oven, which the air fryer developed from, with a
1.3kW element which is on for about a third of the cooking time. There is no warm-up period, the element runs a bit more from cold for two or three minutes. The halogen has an 11 litre borosilicate glass bowl, which is probably a significant part of the cost, which the air fryer doesn't have. We're now on the third, over more than 14 years. We use the kitchen built-in oven about twice a year, for major cooking, and the halogen oven most days.The big gain is convenience, particularly fairly short jobs which don't have that warm-up time added on. It's also easy to see what's going on inside, with a nice, bright 1.3kW lamp on some of the time. And while most built-in ovens are 'self-cleaning', this doesn't apply to splashes and spills, which are a pain to remove from those surfaces. Smooth glass is pretty easy to clean, usually with just a wipe with a damp cloth.