With the updated app, users can spin the tablet device sideways entering into a new UI where on-screen game controls appear and users can play games. While is not as good as an actual Xbox controller, that's still pretty handy and interesting for people interested in one of these devices.
The benefit of a dual-screen device for this type of mobile is that you no longer have touch controls over the top of the game making the user's thumbs getting in the way of seeing important action on-screen. If dual-screen or foldable devices ever catch on, this is a much better way to play Xbox games without a dedicated controller.
Microsoft also tweaked the rest of the Xbox Cloud Gaming experience to work better on the Surface Duo. Some of these improvements include making it easier to view content, move through menus, and addition of columned layouts.