The Victron VE.Bus Smart Dongle is the Bluetooth accessory for Victron's range of inverter/chargers: Multis, MultiPlusses, MultiPlus-II, MultiGrid, MultiGrid-II, Quattros, and its series of Phoenix Inverters with a VE.Bus port. When installed, you can use the VictronConnect App to monitor operation and also operate the system, e.g. change the input current limit as well as switch between Off, On and Charger-only modes.
For monitoring and configuration, this device is a great alternative in caravans, campervans, smaller yachts and motorhomes where a full-blown GX device (like the Cerbo GX) may be a step too far.