The Victron VE.Bus Smart dongle is two products in one:

First of all it is the Bluetooth accessory for Victron's range of inverter/chargers: Multis, MultiPlusses, MultiPlus-II, MultiGrid, MultiGrid-II, Quattros, and their series of Phoenix Inverters with a VE.Bus port. When installed, use the VictronConnect App to monitor operation and also operate the system: change the input current limit as well as switch between Off, On and Charger-only modes.

Secondly it can work as a Voltage- and Temperature-sense device for the inverter/charger. This works with all models.

For monitoring, the device is a great alternative in caravans, smaller yachts and motor homes for which the Color Control GX or Venus GX are a step too far.

It also adds Instant Readout to the VE.Bus product and displays the inverter/charger's key data on the VictronConnect device list page without requiring a connection to the product. This includes visual notifications of warnings, alarms, and errors, allowing for at-a-glance diagnostics.