@xurizaemon #RocketChat worked nearly the same, from the time I use it via mobile browser. That is a +.
Yes, vendor push networks are a concern. I forget the details, but there are 3 or 4 failure points, where the content is leaked to those services, and degrade UX if one tries to make it more private.
Google and Apple convinced all the push apps that sending "postcards" was the best practice, and that is not acceptable. ^_^