It barely ever works, the signal is bad, the ringtone you hear is not because the phone of the other person is ringing, it doesn’t always connect you properly, there is 8 times out of 10 a delay.
And what’s worse is you can see when the other person is online and avoiding your call which causes misunderstanding. In general if you call a mobile normally, if it’s not a good time to speak you can call someone back. On wats app you’re there “online” not picking up the call.