They need to finally release the usernames feature. That will probably make it much more usable. At some point I managed to convince some of my friends to use signal, but ever since they removed sms support, even I don't use it.
They should have waited for usernames to remove the sms support.
I am honestly very disappointed by documentaries in general. Rarely do I find them informative enough or not biased. They are generally made for the masses who know 0 (or even less than that?) about a subject.
If your goal is education, I suggest a book or a course. Now, for motivation and just "time wasters", they are fine.
The one documentary I watched and enjoyed was alphaGo. It was nice feeling the stress of the match and seeing how they handled it, the setups and whatnot.