I'm not knowledgeable about air fryers, so I can't really comment there, but slow cookers / crock pots are fantastic and in my opinion, should be in everyone's kitchen. Maybe I'm biased, though, because I really like soups and stews and sauces and things, which they're great for. Not things you'd cook in an oven, and my stovetop at least doesn't have any kind of timer mechanism.