After having narrowed down the selection to three candidates, I ended up going for a middle of the road one.
Candidates were:
Uten Electric Hot Pot Grill:
https://www.amazon.co.uk/gp/product/B08PF6QQB4/ (not really and air fryer, but relatively slim and both top and bottom contain heating elements).
Salter Aero Grill Pro (6l, EK4549):
https://salterhousewares.co.uk/aero-grill-pro-air-fryer-and-grill/
Ninja Foodi MAX PRO (AG651UK):
https://www.amazon.co.uk/Health-AG651UK-Cooking-Functions-Plates/dp/B09D3SDZ4H/
I ended up going for the Salter Aero Grill Pro (I got mine on sale + with a voucher it came to a total of ~£90), as I wanted to know what temperature each setting corresponded to and with the Uten, it would be a guessing game until I'd have it in hand.
The Ninja seemed a bit too much money and from the YouTube videos I've seen, Ninja devices have really loud fans. I don't expect a silence if a fan is involved, but it seemed like other devices could do better, if mostly from InstantPot (I haven't really seen it compared to other brands much).
I found one review saying the Salter is fairly quiet, so I'd thought that in the worst case, it would be as loud as a Ninja while doing about the same job at half the price of their cheapest air fryer grill.