Apart from the different visual appearance, the two devices differ in the sensor technology used.

The BS 430 CONNECT has highly sensitive stainless steel electrodes with which it delivers precise measured values.

For precise measurement, the BS 440 CONNECT has high-quality ITO electrodes that are vapour-deposited wafer-thinly onto the noble surface and are therefore hardly visible or noticeable.

The BS 440 is therefore the premium model if you like.

Couldn't have answered better than Brimstone. Thank you =)