I've used WhatsApp when traveling overseas as it was preferred by our group for messaging, vs text messaging (due to fees mostly)
But I would not use it or trust it otherwise.
I actually tried to create a lurker/pseudonym FB account last week, in order to get around their persistent request to log in while monitoring some local pages. After "following" six of them, it declared I was a spammer and stopped me from interacting with anything else.