What questions do I ask my installer beforehand?

Before the appointment, find out how many groups your fuse box has and which group supplies which room, so the installer doesn't have to guess. Discuss which four groups the module will control and watch out for edge cases such as a shared washing machine or a socket you use yourself. Also ask whether the fuse box is accessible enough and whether the wiring is physically separated. If you can't find a group that exclusively serves the guest, a small renovation is needed first before a metering module makes sense.