What it is
An MCB is the breaker in your distribution board that protects a circuit. A Smart MCB is the same thing with the app added, so you can see whether a circuit is live and switch it on or off without standing in front of the board.
That is more useful than it first sounds. The distribution box is usually high up, often in a passage, and frequently behind a locked panel in a rented flat. Being able to check it from your phone — or from another city — removes a whole class of "is the power actually on?" problems.
What you can do
•See the ON/OFF status of the MCB in real time.
•Check whether the connected circuit is powered or disconnected.
•Know immediately if the MCB has been switched through the app.
•Monitor the circuit remotely, without opening the distribution board.
•Keep an eye on critical circuits while you are away from home.
Real-life example: A family leaves for a fortnight and wants the geyser circuit dead but the fridge circuit live. Both are checked from the airport, and the geyser circuit is switched off from the phone rather than going back upstairs.