Local conditions
Humidity is the whole argument
Wood Moves. This Coast Makes It Move More.
Brisbane and the Gold Coast sit under mean 9am humidity at 65% or higher for most of the year. Timber takes moisture out of that air and gives it back, and a slat that does it repeatedly eventually keeps some of the shape. In a room with air conditioning and a door that gets opened, the movement is small enough to ignore for years. In a bathroom, an ensuite or a closed-up laundry, it is not.
The second half is the sun. East and west glass on this coast takes low direct sun that an eave cannot reach — the Your Home guidance on shading is blunt about that orientation. A timber slat on unshaded western glass will fade on the face that takes it, and it fades unevenly because the slats tilt.
So we ask which way the window faces and what happens in the room, before we talk about timber at all. Anyone who does not ask is quoting a slat, not a window.