Ninja
Foodi Dual Zone Series
Dual zones excel, but bulky with small baskets.

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Yup. Def need separate air fryer & pressure cooker. The insta-pot fryer lid sucks.
The Instant Pot Pro Crisp has an airfryer that is free from BPA, PFOA en PTFE (Teflon). It has a "ceramic" coating. I think PTFE is the material that is dangerous for birds. I don't know about the other models, you might take a look. (Instant Pot also has stand alone airfryers )
I love my InstantPot Pro Crisp. It does all the things an InstaPot does and has an air fryer attachment. I needed a new toaster oven because mine just died, so I got an Emeril French Door 360, which also has air frying functionality. We'll see which one I end up using the most. I love the InstaPot, but I literally have to switch out the top as that's where the air fryer is vs. this new one, I'll just need to load the food in and tell it to air fry. I just got the toaster over replacement, so time will tell. I still have yet to wash all of the different trays that come with it to use it. But I'll test run it later today with Trader Joe's brand tater tots. I'm not sure why, but with that brand I found I have to adjust the temperature up and cook a little longer for them to crisp up. I'll see how this new air fryer handles it. And I realize I didn’t answer the why part of your question. The more expensive ones give you more versatility. Like I can use my InstaPot for stews and steaming. I’m using the Emeril right now for those tots I mentioned, and I’m pleasantly surprised that they’re browning up very nicely too. I might eventually try the rotisserie, but I’m more of a dark meat leg, thigh, and wings gal. I’ll probably still with the grill for that.
I have one and the air fryer part is decent, but it is not going to replace a dedicated air fryer. It works best for smaller batches or things like reheating leftovers, wings, or roasting veggies. The biggest limitation is space and airflow since the pot is deeper than a normal air fryer basket. If you already want it for pressure cooking and the air fryer is a bonus, it is nice to have. If air frying is the main goal, a standalone unit still does that job better.
Lots of stuff on YouTube. Start here: https://youtu.be/WbvqDH0cWiU?si=Q9KY7mZQag-cTmJj I have one. It works well but it is not as easy to use as a drawer type air fryer. With it being deeper it's easy to burn your forearms when you're turning things. I got tired of burning myself and bought a Cosori Turbo Blaze. Pro Crisp is great and it does air fry well it just didn't suit my needs. Bear in mind I'm one person, other people may have had a totally different experience.
Don't know if you have the 6 or the 8 quart pro, I have the 8 quart. I hear you about space. I ditched the included non stick insert and started air frying right in the inner pot. I bought a set of three trivets of varying heights. Bought a 9 inch round cake cooling rack to put on the trivets. It fits the pot edge to edge and greatly increases airflow. It also allowed me to cook much more food at once.
It's a grill, first and foremost. The air fryer feature is an added bonus. I have a Ninja IG651 grill, I've used it for years, works great for both functions. Nice large, spread out air fryer basket to reduce the ability to overcrowd. Your option should be similar. Don't bother with that Instant Pot.
Ninja
Foodi Dual Zone Series
Dual zones excel, but bulky with small baskets.

COSORI
Turbo Blaze 9-in-1 6QT
Effortless to clean and quiet, but no viewing window.

Ninja
Foodi Air Fry Oven Series
Unique flip design, but shallow and air frying debated.

Typhur
Dome
Self-cleaning and quiet, but expensive with shallow interior.

Breville
Smart Oven Air Fryer Series
Great oven replacement with large capacity, but poor air frying.

Ranked #1
Ninja - Crispi Pro 6-in-1 Countertop Glass Air Fryer

Ranked #1
Breville - Smart Oven Air Fryer Series

Ranked #1
COSORI - Turbo Blaze 9-in-1 6QT

Ranked #1
Ninja - Crispi Pro 6-in-1 Countertop Glass Air Fryer

Ranked #1
Ninja - Foodi Air Fry Oven Series