We got one as we were undergoing building work and without a kitchen for several months. We got by with an airfryer and a microwave. It was a lifesaver.
Moving forward, we will still use it, as it's better/quicker/more convenient for some things.
It's useful if cooking sides (e.g garlic bread/samosas/spring rolls/part baked baguettes) to pop them in the airfryer without having to waste time and energy pre-heating a whole big oven just for a side.
It cooks a whole roast chicken (and is super succulent) in about 50 minutes. Not really worthwhile if you're cooking a full roast for a family as you'd have the oven on anyway, but if you just want roast chicken with new pots and salad, it's quicker, cheaper and easier.
It's great when a teenager just wants to make themselves a single portion of oven chips/nuggets/chicken kiev/fishfingers.
Bacon cooks in 8 minutes and is delicious and cripsy - perfect for an easy bacon sandwich for breakfast. Sausages cook in about 10 minutes. Much quicker, less messy (no fat splattering) and superior results to grilling.
I don't think there's much that it cooks that couldn't be done another way, but the results are often better and quicker than conventional cooking.
It's amazing how many things we've managed to cook in an airfryer - fajitas, kebabs, boursin stuffed bacon wrapped chicken breasts, roast dinners, chillis, curries. It's not just for breaded food and oven chips! Obviously it'll suit some families lifestyles more than others, but I'm glad I've got it!