First of all it is the bluetooth accessory for Victron's range of inverter/chargers: Multis, MultiPlusses, MultiPlus-II, MultiGrid, MultiGrid-II, Quattros, and 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, and is especially useful in combination with the MultiPlus-II, as it does not have on-board terminals for Voltage- and Temperature sense wiring
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.