Like any plain old resistive heater, about 100% of the energy put in is turned to heat. That does meet my definition of 'energy efficient', as do quite a lot of other kitchen appliances. Its heat losses to surroundings are much less than the main oven. I expect that on convenience and so on it is less good. This one is just about scraping it to 'sufficient' cooking temperature from an input of about 0.72kW, which is probably better than most appliances. From the photo, you can see that it is a bit small and that cake wasn't going to last for long. How much time does it take to cook for three in the air fryer by comparison to the main oven ?
A measure of 'efficiency' is 'how hot does it get in the kitchen?. Boiling over a gas flame cooker is quite poor like that, with half of the flame heat missing the pan, and half of the pan contents not being dinner.
If you have children, this Mini Oven is too small for a hot meal for three of you, so I'd suggest that you aim to get to sufficiency by a different means to the one appliance for one person. You cannot run a 2.6kW full sized electric oven for free while less than 2.6kW is available, so if you wanted oven cooking for free around noon on sunny days, that would need at least 4kW(peak) or more of solar panels for only the best days of summer to be free. To run a full sized oven for free as often as my mini oven can, should need no less than 9 kW(peak) of solar panels, which is more than you'd be allowed to have on one roof, and 3x more than could ever possibly be fitted in the limited space of my roof. The best that you can do is to get as much solar power as will fit on your roof.
If you wanted to design your neighbourhood to have sufficient provision for yourself and children to get a hot meal most days, then your neighbourhood needs access to at least enough renewables and without the obligatory gas fired backup electricity which makes everything so expensive. I'd place a lot of the needed renewables where you and the kids are most usually going to be at noon, so that would be whole roof solar at the office and at the school, with new large electric cooking machinery at both (most school dinners equipment will date back to North Sea gas; they might be due to get sponsored for a renewable electric retrofit). To improve utilisation from 195/365 days per year, school dinners machinery should need a Saturdays and holidaytime 'lunch club' running the school dinner kitchen more often than only school days, and possibly adding a third sitting 'pensioners lunch club' after the 1pm bell when the kids have gone back to class. Maximum efficiency of hot food provision should keep the ingredients mainly local, (more potato, more peas, more carrots than 21st century average; less imported beef, less of a lot of the fancier things) and absolutely avoid parasitic losses such as sending money overseas for franchise fees, canteen rent, printed paper branding, and extra costs like that which do not contribute to nutrition. The last large scale saver is to seperately meter and designate the canteen as a 'schedulable OFF' lower priority load; that the school cook has authority to designate today a 'sandwiches day' or anything else which will use very little electricity in forecast 'dull doldrums' weather. With such planning, future meals need not see ever increasing prices.
So for best £/meal and CO2 per meal at best nutrition and minimum capital investment per person, I say that economies of scale are necessary, sensible forecast based planning should be necessary, and those could help a lot more than would my undersized single person mini oven.
