You may not even need the app. Zulip on Android Firefox is a better experience for me than the app, personally. (Tho the web version was, oddly, severely laggy in mobile Chrome the one time I tried it, some time ago...)
The UI is somewhat confusing; also, it seems designed to give a view of particular, selected streams and topics of interest, and doesn't always seem to keep up even with those -- but volume on my server is low enough that I want "all messages", and if there's UI which does that reliably... it's not signposted well enough for me to find it before my patience ran out.
