I find myself these days hesitant to even consider any private messengers if they don't have the option to verify which devices/keys have access to your messages. #Signal, #XMPP / OMEMO, #Matrix, hell even Facebook Messenger's E2EE chats let you verify which devices can read your messages. If you're encrypting your users' messages, but they can't verify whether a rogue device has access to their messages, then why even bother encrypting them?