Facebook missed a big opportunity with end-to-end encryption in Messenger
Unless you don’t care about videos, group chats, and can remember to turn it on for each new chat.
Videos and GIFs aren't supported. Group chats aren't supported. Other platforms aren't supported — for example, you can't send a self-destructing message on your web-based Messenger, only on an iPhone or an Android phone.
Add in that you have to remember to do it for each conversation and that it's not super clear how you go about turning it on: "You need to tap on a nondescript "i" menu item (I'll bet you never used it before), and then choose "Secret Conversation" to start an end-to-end encrypted chat. There's another way to do it: Hit the big "+" in the lower-right corner when you start Messenger. Choose "Write Message," tap on the tiny lock in the upper right corner, then choose a name from the list below. Are you going to remember to do that every time you start a new chat?"
We should all just install Signal: https://whispersystems.org/
For those looking for a comprehensive overview on staying secure check out Cloudwards great article on how to encrypt SMS messages.