I've had two, and they're brilliant. Particularly for cooking for one or two - they're just tiny ovens really, and so use far less electricity than heating a whole cooker oven.
My first was a Wilko cheapy, just to see how I got on. Brilliant! One day the cooker oven blew up half way through a small joint, and I finished cooking the meat very successfully in the air fryer.
My second was a Tower, and was equally as good.
My third is currently packed away pending a house move in a couple of weeks.
Two caveats:
1. in both Wilko and Tower, the non-stick lining began to peel off the base. As it happened to both, I'm disposed to think it was my fault, though I don't know why.
2. In both cases they only had one hour timers, so if I was making anything that took longer, I had to be around to turn the timer back round again. On the other hand, this makes them quite useful for people who might go off and forget they've left it on.
Best things I've ever bought for the kitchen!