The key handling is (as always with this big corp "crypto") murky to say the least.

FB effectively still controls the encryption keys.

Coincidentally nobody of the usual suspects complained that "the terrorists are going dark".

Putting this facts together I'm assured the crypto can be broken at will.

It's Facebook! How can you trust them?

If you honestly believe them then I've got a bridge you might wanna take a look at...

Is it opt-in? If so that means ~0% of people will be using it, so all your chats will still be backed up non-e2e by the other side of every conversation.