On its 10th anniversary, Signal’s president wants to remind you that the world’s most secure communications platform is a nonprofit. It’s free. It doesn’t track you or serve you ads. It pays its engineers very well. And it’s a go-to app for hundreds of millions of people.
You do if third party clients aren’t possible? You have control over what client the receiving end is using.
But apparently third party clients are possible, so it’s moot.