Removing the rejected tag because Threema no longer obviously doesn’t meet our criteria, but I’m still not sure recommending it is the right move either. In the wise words of @dngray:
The general consensus since the cleanup is we don’t want to be recommending a gazillion instant messengers which really offer nothing over anything else. Centralized messengers are really not that special.
That being said, I can see the value in a polished (unlike SimpleX) messenger with non-identifying identifiers (unlike Signal).
I really still have a hard time getting over it being a paid app. I would pay for such an app if I had a use for it, but the number of my contacts who would pay for such an app I could probably count on one hand, and I feel like that means it’s not really going to drive adoption of private-by-default messengers the same way Signal does 
Two things I would like to know from people who like Threema:
- If Signal added usernames but you still had to register with a phone number (which would not be shared with your contacts), would you use it instead of Threema? (Especially because Signal is $0…)
- If Signal added usernames and let you register without a phone number too, would you use it instead of Threema?