It was consensus between colleagues/friends. And because you still need to trust open source software as well. I certainly don't have the time to review the code, and the "somebody else will do a thorough code review" fallacy should be well known by know. As said, Threema at least had a name attached to it that I somewhat trust.
Telegram for example doesn't exactly tick the "not as questionable" box for me, not least because it isn't entirely open source either, but also because I always find it weird if someone is pouring money into software that is available for free, with no obvious benefit for them in return.
Telegram for example doesn't exactly tick the "not as questionable" box for me, not least because it isn't entirely open source either, but also because I always find it weird if someone is pouring money into software that is available for free, with no obvious benefit for them in return.