I know that they allegedly use the Signal proctol, but I find it hard to trust since not even the client is open source, even if their protocol is what they say it is, the keys could be harvested without issue, which is probably what happens when you use the reporting feature that allows them to read a piece of the message history, and they could still log your text input while typing. Of course, no way to verify neither their claims nor our theories.

#but no one is using them

Agreed, I did convince a fair few people, but it's not always easy