charlatans? You mean like when Facebook claims they have implemented the signal protocol but then scan your messages for keywords in order to disable encryption for governments? There is no way for you to check my claim nor Facebook's as it's closed source.

Same goes for threema which will shortly be required by Swiss law to comply with Büpf as they will reach a size requiring it. It's closed source, we can't check what they are doing. Their external security audit was a long time ago.

At least with telegram if I install the android version off fdroid it is compiled from source and I can verify that.

I can gets users to switch to telegram, I can't get them to switch to signal. There is a trade-off but I would argue telegram over whatsapp anytime.