If you use a toaster oven regularly, you may want to buy the combo so that you don’t have two appliances.
If you will only use the air fryer, the standalone air fryer may be the better choice.
We received a very simple air fryer as a gift. However, we used it so often and it was smaller than we needed, we bought a another one. We ended up with a Ninja brand combo. It has a lot of functions, but we mainly use the air fryer, toaster, bake, and warmer settings.
Ours from Costco - we use it everyday!
https://www.costco.com/ninja-foodi-10-in-1-air-fryer-oven.product.4000105708.html