What could be the function of three components of this surge protector?
The round component on the right, connected between Neutral and Protective Earth, is a gas-discharge tube. It presents a very high impedance until its voltage rating (many times the peak line voltage) is exceeded.

Yes, the item on the lower left is a MOV, as you suspected.

The larger square diagram on the upper left is a puzzle. If you squint just right, you could interpret it as some sort of circuit breaker, intended to open if the MOV fails shorted (which they tend to do).