If you have not used this type of device before, they are a lot more than a fryer, they are actually an oven. They have been around for over 30 years, it is only recent tech advances and cost of energy and cost of oil which have made these trendy. They are esseentially a high power fan type oven.
They cook a lot quicker than a conventional oven because its a small space to heat and the fan creates a lot of air flow. You can also reduce the amt of oil you use.
For example, roast potatoes cook, depending on how large you cut them from 10 to 20 mins. Which is a big saving on the electric. When you by an air fryer, buy an oil sprayer as you will often use a few pumps of oil. This makes things crispy. I brought one from Amazon. When you do buy a spray make sure it is for oil, I wated money on a few which could not handle veg oil.

This actual device, has some great features, it has lots of presets which are useful guides, like other devices of this kind, I own 2 air fryer ovens, this bin style and one which is more like a normal oven and has a rotisery.
This has 2 advanced options which is match cooking, used when cooking things which need the same time and temp in both bins. Also match finish. You set the temp and time for each bin, and press this button they will finish cooking at the same time, which is really handy.
Something else about a bin style fryer, you need to take the tray out and give it a shake from time to time, which you may think is a pain. In reality its not. The cooking time is so much shorter than a normal oven its no big deal to pull out the tray and shake it. Im normally preparing and cooking other parts of the meal whilst the oven is cooking so Im in the kitchen anyway.
The build quality feels good, I did look around in shops before buying some of the cheaper ones do not feel they will last very long. This one feels good.
Something else to check is the quality of the non stick. That is key, according to a CH4 documentory I watched about air fryers. They did a test on many models and this one rated very highly. On the cheaper ones the non stick often peels off after only a short time and use. This one looks to have a good quality of non stick, thats by observation and what the test said in the documentory.
The cheapers are ok, but think about how long you want them to last and how often you use them. The mid price may be better value for money.
Another thing about air fryers is they cook so quickly and are so easy to use, I find my self using it a lot more than I would have ever used a normal oven. In many ways its taking over from the microwave. Especially when reheating things, i.e. left over pizza comes out nice and cruncy rather than the limp slice when heated in a mirco wave.
This has a preheat button which is excellent and further reduces cooking time and makes the food cook better. Preheating a normal oven is always a good idea but takes in mine, 10 mins. This air oven preheats up to 180C in 3 mins which is a lot more convienient and costs a lot less.
I cannot stress enough but the reduced cooking times and the money you save on oil and elec.
When cooking normally you would use a good glug of oil for roast veg, in this fryer a few pumps of the spray is all you need. Which also means its better for your health.
I did look at the ninja in a real shop and compared the 2. The ninja you appear to be paying a lot for the name. The quality did not feel as good as this device.
I would also reccomend, buying some liner trays, again I brough them on Amazon they are made from a type of paper and makes cleaning very easy. Ive been warned not to use normal baking or waxed paper in an air fryer as it may fly up in the air flow and is a fire risk. This warning applies to all air ovens/fryers.
I also brought a wire rack on Amazon which lets be double decker things. The one I brought was around £14 is has a stand frame and also a 2nd frame with 4 skewers. It works well for kebabs etc.
Overall this is a great device and is priced well for what it is. As I said I did look at some which cost a lot more and decided on this one.

Takes very little time to get used to how to use it and it really is great.
The two baskets can be used independently or they can be set to finish cooking at the same time.
There is a great 3 minute warm up function then a whole selection of preprogrammed functions to use. I was initially disappointed that there was no way of putting in your own functions but quickly realised that it’s so easy to alter the temp and time of each programme that it really isn’t an issue.
We use liners in with our drawers so that the drawers don’t need washing up every time that we use it which is great as it means less washing up too!!
Would definitely recommend it, especially for the price.