The real difference is speed and consistency, not magic. An air fryer heats up in like two minutes and crisps things faster because hot air circulates way tighter in a small chamber. Your convection oven does the same thing technically, but it takes longer to preheat and the heat distribution isn't as intense in that bigger space. If you're cooking frozen fries or chicken wings, an air fryer gets them done noticeably quicker and often crispier without much fiddling.
That said, if you already have a decent convection oven and you're happy with it, you're not missing out on anything revolutionary. It's more about convenience than results. An air fryer is really useful if you cook a lot of small portions or want fast weeknight meals, but it doesn't do anything your oven can't do eventually. The counter space thing is legit - these take up room, and if your kitchen's already tight, sticking with what you've got makes sense.
I'd say skip it unless you're cooking for just one or two people regularly and speed matters to you. If you're feeding a family and your oven works fine, that's your answer right there. The hype is real for specific situations, but it's not a must-have.