dirksche What I don't like with Signal: you have to solve a Captcha before using the app. So you have to connect Googleserver. I don't know what information will be transmitted, but this coercion is a pain in the a..
If I am not mistaken, Threema is a paid app, so you have to actually buy it somewhere (Play store?), so there are some information about payment involved and also some e-mail account. If that is the case an user has to also get in touch with servers of Google. If all above is correct (I admit I haven't looked pass the payment info), I would be much OK downloading apk from Signal.org, than to provide all necessary information to buy "anonymous" app that in the process gathers even more information about the user.
Nevertheless, anything that tries to avoid Facebook, Apple and Google deservers (IMO) at least little praise :-)