oh, and one other thing - there's also real value to independently published public security audits of the crypto to pick up on things like WhatsApp's retransmission 'bug', at least as of a given snapshot of the codebase. E.g. https://www.nccgroup.trust/us/our-research/matrix-olm-crypto... for Matrix or https://conversations.im/omemo/audit.pdf for OMEMO & Conversations.