It's largely from disappointment - I assumed initially that they were designed to save oil vs. a deep fryer, that they blasted jets or misted oil over the food. That I think would be novel and interesting.
As it is, if you have an oven already, the RoI is too long to do it on a cost basis. Maybe there's an argument of time-saving as they pre-heat a smaller box quicker? Hardly takes long as it is, I think that's a stretch.
If you don't already have an oven, then yes, if the capacity is not a problem then it's a great option, they start cheaper than bigger ovens... Obviously I suppose.
(I suppose I shouldn't have generalised so much above - I was speaking from my experience in the UK. Other than perhaps a tiny studio flat (single room apartment, no separate bedroom) I would think it's pretty much unheard of to rent somewhere without one here; buying it would normally (almost always) be included, but if not there'd be an obvious gap where yours or your newly purchased one would go.)
Anyway, in the very first line of my comment I said it's the marketing that I have a problem with; I have 'tried' the marketing.