The back of my Zenfone 9 (Midnight black) is already worn after 12 days. I do not mean the texture, but the lettering. Only "ASUS Zenfone" can still be recognized to some extent. The text under the camera is completely gone.
Of course, this does not change the functionality. However, you can definitely expect something better for a smartphone in this price range. Is Asus planning to do something about that? E.g. a (free!) replacement for a more resistant back?