But you are not safe to discuss anything on most Chinese smartphones regardless of the App, because common input methods in China (optimized software keyboards) send all your keystrokes to their servers.
Freenet actually warns you about that during installation.
Freenet currently takes the simpler route of suggesting to use the phones' IME (because that isn’t already proven to send all keystrokes).
It is likely that using Freenet in opennet-mode can get you on a watchlist — but you’re already on that if you wrote here.
There have not been report of actual tracking of Freenet in pure friend-to-friend mode, but there are too few people using it exclusively in that mode to be sure.
Freenet actually warns you about that during installation.