I agree that we only have the choice between the devil and the deep blue sea concerning mobile OS. But why is iMessage so great (asking as a non-apple user)? I

I agree that we only have the choice between the devil and the deep blue sea concerning mobile OS. But why is iMessage so great (asking as a non-apple user)? Is it even e2e? Great alternatives which are not locked into a specific OS are Signal, Threema, and Matrix. Specifically, Matrix -- which is also a protocol -- looks quite interesting to me. Similar to email, you can choose your client software. You are also free to set up your own matrix server but you don't have to.