The AL-KO Robolinho (300 m²) generally works with a boundary wire to define the mowing area. Without a boundary wire, it cannot work safely and efficiently as it cannot recognise the area to be mowed. The use of a boundary wire is typical for many robotic lawn mowers to exclude fixed obstacles and define the mowing area.
It works, it is waterproof, but it does not have a sensor. It would be better to have it to NOT cut the grass when it rains, but it doesn't have one. So you can either tell from the APP not to mow the lawn (when we see that it is raining) or cut it and be patient.