Use Signal,

It’s what I advice my clients to use and it’s much cleaner and easier due to being less bloated.

Networking effect

People use whatever is most popular even if its the shittest thing such as Facebook.

Only time people will care is when it personally and tangibly affects them.

For Facebook/whatsapp watomatic can be used to remind people you are leaving or such.

Closest option is watomatic but it only works with whatsapp and Facebook messenger. There are talks about expanding it to support other platforms

So the whole security and privacy claims are purely marketing.