We have a double oven (I made the cabinet for it), Mrs S uses the top oven a lot but when she is using the main oven she cooks in bulk and freezes. Then again we have two chest freezers and two uprights, one under counter and one full height. So cooking in bulk is not a problem for us but not for everyone.
I used the halogen oven for the best part of a year and found that it was limited. The Air fryer is more generally useful. I managed to get an 8.5l double drawer model with crisping trays. It cost £79 which is about twice what my halogen oven cost but I find it much more useful.
Mine has smart finish and match cook so you can cook two different things and have the cooker finish them at the same time. You can only do this with an oven by setting timers and putting things in at different times. Granted it is not perfect at everything but it is versatile for what I need. Also the drawers are coated with good quality teflon so cleaning is not an issue and I also have some silicon inserts to keep some of the cooking out of the drawer or even to allow me to fast switch without cleaning.
It is a fad, I agree. But it actually works in a lot of cases and it has got me away from pre packaged food in the microwave. Not that it is helping with the diet, I'm eating too much.....
Our kitchen at home is 2/3 the size of this entire flat. So options are different.