I also have Signal but found out a Twitter IT Security agent helped start it up. Now it’s said to be monitored by Twitter.
It didn’t help to see Dorsey endorse it.
Twitter CEO Jack Dorsey says download Signal as US protests gain steam
Signal is the better option for true end-to-end communication, regardless of the rest of your concerns.
Signal is open source. You would be able to get the source and build it yourself (which also means you can modify it if there is something you don’t like). Thats how it used to be, not sure about now