Bigger screen than a regular android phone. Especially because your 6" 21:9 phone means a 16:9 picture on it will only take up ~5".
Also better controller. Those mounts for a phone on a regular Xbox/Playstation controller always make it too top-heavy since your phone has to be on top of the controller. And I love the idea of a full-sized controller over a Switch or even Steam Deck’s tiny buttons that just aren’t comfortable.
I’d probably only be interested if it lets you run actual Android stuff though. Have you seen the Logitech G Cloud gaming handheld? That one’s even more expensive, but it does run local games too.
why anyone would prefer that over simply using a regular Android phone with a good controller
I always think this is funny because that sums up /r/sbcgaming