We bought one last year.
We were able to try one for a week to see whether we'd get on with it, as we're members of Bath's Share and Repair scheme, and ours gets a lot of use.
It's not the answer to everything but with only two of us it means that our main oven is used much, much less - saving us money and reducing pollution in the process. It's basically only a small fan oven, but that means it gets up to temperature quickly and is less expensive to maintain the temperature.
It's great for a lot of things you'd do in the oven and some things you might fry - oven fries, baked potatoes, roast veg (such as cauliflower or kale), Mediterranean veg (peppers, onions etc), nut roast, sauté/parmentier/roast potatoes, ribeye steak (haven't tried fillet steak yet), burgers, sausages etc etc.
It's a very, very handy addition to the kitchen and with the reduced electricity use it will easily pay for itself in time.