I don't think you can do anything that is freshly battered. Batter starts to harden as soon as you drop it in hot grease. With no grease in an air fryer, you would just have a pool of batter under the basket and naked onion rings that have been air fried. I would think that frozen items such as onion rings, fish sticks, and cheese sticks from the freezer section would do pretty good, mainly because they are pre-fried at the factory and the batter thus holds up in the air fryer.
An air fryer is really just a compact convection oven. It circulates super hot air around the food. Being a small space and the hot air gives the look, taste and feel of fried foods, but it still isn't fried. I suspect things turn out okay, but nothing really will give you that true deep fried flavor and crunch.
I have considered getting one, but really don't have the space for it and am not sure how much I would really use it. I do love our electric pressure cooker and use it a couple times a week. We also have a small deep fryer for those few times we want something fried, which is rare. We actually like chicken wings out of the pressure cooker. We just put them in the oven for about 10 minutes after they are done to help crisp them up. They would probably do better in an air fryer after the pressure cooker.