See Netguard…
As best as I can discover Signal,
You give them your addressbook and your phone number, you’ve just exchanged the name of the company from Google to OWS, good job lol
I’d bet he doesn’t even use that…just a ruse 
You trust them to not log anything, but you can’t verify anything, meh
Yeah…but they can record your credentials and access your inbox, also if you send/receive to/from gmails accounts then both Proton and Gmail can read your emails
It’s not because Moxie doesn’t want it here, basically it’s a closed silo messaging app based on phone numbers…oh and some source-code released. It’s a pain to host your own, and if you do you can’t reach Signal users anyway. Read more here: We can include Signal in F-Droid