They can be completely serviced from the button cutout - you can remove any parts through it (it was designed this way). I think almost all newer toilets in Europe are wall mounted. It looks better, it's very quiet (refill), saves space and works exactly the same... Here is an example video how to take it apart https://www.youtube.com/watch?v=es8SJ-1CFcU
It's serviceable, but it looks harder to access than a visible-tank toilet. At the 3m mark in the video, my hands are instinctively cramping just by looking at that tight space.
The difference is like working on a car in the 70s versus a Japanese compact car from the late 90s.
This and they are basically maintenance-free. I think most people don't know that these things are serviceable at all. They also often have two buttons that release a different amount of water. Good for the environment and saves you money.
