Electronics repair site iFixit just released a repair report on the ASUS ROG Ally gaming device, and they say it's easier to open and repair than the Steam Deck.
iFixit, through their website and YouTube video, says that in terms of opening and repairing this ASUS console, upgrading and changing the internal components of the ROG Ally is easier.
Among the examples given is in terms of battery replacement. iFixit says that the battery on the ROG Ally only requires the user to remove a few screws, but for the Steam Deck, the battery component is glued to the hardware frame. Meanwhile, it's also easier to move other components such as buttons and controls on the ROG Ally compared to the Steam Deck.
For both of these consoles, the hardest part to open and change is the display part as it needs to be glued in place to ensure that it doesn't move when in use.
However, iFixit also said that although the ROG Ally comes with better opening scores and improvements, one issue this console faces is the lack of official or third-party components for now. iFixit does sell a number of components for the Steam Deck, but for now you can only get ROG Ally parts from opening other consoles.