Which cistern to choose?

Depending on the make and model of the cistern, some have more access than others. You can usually work on these items , but the advantage is really with it being concealed giving you more space in the room.

Most in wall cisterns are designed so that all components can be replaced by removing the flush button and mounting plate, geberit are a good quality piece of kit.

Grohe concealed cisterns are easily accessible through the flush plate.

The key to a concealed cistern is how the design of the bathroom accommodates access for maintenance. Many of the concealed cisterns are very plastic....and flimsy....and from my experience they seem to be an inferior design to a good old fashioned ceramic / porcelain toilet cistern that's solid. In my bathroom designs access is always accommodated into it to be able to get into the hidden cistern along with an access hatch / panel to get to an isolation valve at low level in an inconspicuous position near the pan so as not to compromise on finish appearance. If the hidden cistern has a tile shelf for instance then a split in the tiles and underboars is built in so that it can easily be removed with minimal destruction to enable access. There's nothing wrong in a hidden cistern.....as long as a way of getting in to it is built in.....but also bear in mind that if you've got to build out a wall or alcove to accommodate a hidden cistern then with there being some very slimline compact close couple toilets available.....the actual pan won't be in a different position and therefore doesn't actually save any space. Hope this helps