The old model is not mentioned in the question, but better than an S5 Max would be, for example, the S6 MaxV with the built-in 3D object recognition, it is expandable thanks to the database integrated in the robot hoover by Roborock and can select objects better. The surcharge is not that high.

Roborock S6 MaxV

If by predecessor the S5 without Max was meant, the S5 Max now has a much larger water tank, which is mounted in the back of the device. This tank is the same on the S6 MaxV and S5 Max. Both also have an electronic water pump that allows you to regulate the flow rate in the app. The old S5 only had a passive water tank without an integrated pump, which was attached to the bottom of the hoover. There was relatively little water in it compared to the S5 Max and S6 MaxV.