Seen them on TV when I have been wandering by but have not taken the plunge myself.
There is a phrase along the lines of "a tool that does everything is good at nothing" and while some things might be combined together (air fryers being little more than kettle elements in a box with a fan) that list does not look that useful.
At the same time the backlash against air fryers has me curious; air fryers will not replace various tools and techniques but will get 90% of the way there (95% if you shallow fry some things afterwards that would normally be double fried) which is more than enough for weeknights. To that end the dehydrator will probably not beat my standalone one but I would be surprised if it can't get enough done to note.
Would an air fryer replace a foreman... that is a tough one. I reckon I could pull it off but it is not going to be a drop in replacement.
I am also wary of kitchen gadgets with too many brains. Chips and sensors, and stupid touch screens, when I could have clunking switches and buzzing timers instead is not my chosen path.