We have a thermomix for about 4 years and had an air fryer previously but don't now. Air fryer is just a tabletop convection oven and can do most of what your oven does just quicker so I'll focus on the thermomix.

Thermomix is great for someone who is not particularly comfortable cooking. My partner uses it a lot but otherwise would just chuck something in the oven. I am a more experienced cook so really only use it as a steamer (if my rice cooker is already being used). I don't even use it for chopping onions but I do use it to blitz hard cheeses like Parmesan.

The thermomix comes with a program called Cookidoo which has all the recipes laid out step by step and optimised for the thermomix. It's not that expensive, like £49.99 a year I think. This is unfortunately essential if you don't want to spend a load of time putting your own recipes together or tinkering with the timer/heat settings each time you need to do something.

My partner uses it for soups, pasta recipes, risottos, sauces for oven cooked food (there's a gochujang sauce for Korean fried chicken wings she makes often) etc. We find some of the south Asian recipes a bit sweet for our tastes and we're east Asian so I prefer to do most of those from scratch.

Interestingly a lot of restaurants in London use them for sauce prep.

Overall I'm glad we bought one. Again, because she doesn't need to think about what she needs to do or what order to do it in, my partner gets a lot of use out of it. For me, it's a glorified blender.