Daniel Gultsch's (developer of Conversations
, a very usable messenger that uses a decentralized protocol) reply to Moxie Marlinspike's (main developer of Signal, a very usable messenger that uses a centralized protocol):https://gultsch.de/objection.html
A free and open source Jabber/XMPP client for Android. Easy to use, reliable, battery friendly. With built-in support for images, group chats and e2e encryption.