Wrong, if you are using F-droid, you aren't trusting the dev, you are trusting F-droid and the source code, the dev CAN NOT give you an app that doesn't match the code, and the code can be seen and reviewed by anyone.
As long as the protocol is open and has encryption you don't need to care much about that. Packets on the internet travel through thousands of different machines around the world. You are either using encryption or the whole world is reading your message anyway. There is nothing in-between. If you even want to hide metadata, you would need to use something like Session.
What alternative does the video promote? Trusting Google and the Playstore? Trusting each dev of every app to deliver apks which match the code? I don't want to give the video more clicks if it's scaring away people from F-droid towards worse alternatives.
Have you tried Droid-ify? If not, you should.
Also unlocks a hidden badge: Not worthy.
Paying more for a less durable device is not what I prefer to do.
I would prefer session but messages aren't reliable. They can come late or out of order, if the core functionality makes you trouble you can't make convince other people to use it.
A F-droid client: https://www.f-droid.org/packages/com.looker.droidify/