Steamdeck only can go to 15 w tdp asus rog ally can go to 30 w tdp this is why the power increase.

Steamdeck oled if you want a better battery and a great screen asus rog ally z1 also have a very good screen for LCD but much more power to play games on higher resolution + higher preset but the battery life is a lot worse you will need to be next to a power outlet all the time if you want to play demanding games.

If you want native gamepass games without remote connection the choice is easy go with Asus

Sorry for me it is not clear what does this mean that they wil put a order for the SD oled for you and you have to pay back the difference when you send back the orginal steam deck