I have very recently bought a 7ltr air fryer so finding my way with it. Bought primarily to save on the electricity from using the full size oven. Pros so far: cooks quickly, nice crispy chips and fish in breadcrumbs,, crispy bacon in shorter time than the conventional grill, less lingering food smells, very little pre-heating, easy to clean (no getting on hands and knees to the cooker innards!), has various pre-settings but these can be adjusted or can use it totally manually, and must be saving on electricity overall.
Cons: if having to cook in batches or foods on different sets of temperature - how to keep food hot while the next bit is cooked? It does need its own bit of worktop not too near other things because it gets pretty hot - I've got it pushed back out of the way when not in use, but pull it out into an open space when I'm using it.
I have tried some baking in it as well as it has a bake setting - made some rather nice fudgy brownies. The size of the drawer meant a small 6/7" square tin the largest which would fit. This meant only a smaller amount of brownies could be made - I suppose whether this is a positive or negative depends on whether you are supposed to be eating that sort of thing! After all, it's supposed to be a more healthy way to cook....
I do have a Multi-chef, which gave the option for 7 ways of cooking, (slow cooking, pre-browning then stewing, deep frying etc) but tbh I'd only used a couple of the options and as it has stopped working properly and I have a separate slow cooker I thought I'd give the air fryer a go.