It is extremely useless compared to Whatsapp/Signal. It is not even natively supported in android like SMS. Even in android the only app that supports it is Google Messages (unlike several for SMS). Nobody supports the protocol and everyone uses Google's implementation. Google's client, Google's servers, optional encryption. What is good about it. The only reason for it's existence is to make Google get a leg in the messaging clients after failures with their previous attempts (Gtalk, hangouts, allo). That is why nobody outside the USA would ever bother using it.
It doesn't do anything that Whatsapp/Signal don't. And there is nothing native about it in Android, other than Google Messages is force installed on all devices, and the rich vibrant ecosystem of android SMS clients was killed off to make way for it.