The short version
Gflix has no account and no advertising, and nothing you watch passes through a server of ours. Your sources, your credentials and your watch history live on your device and, if you turn it on, in your own iCloud account.
The one thing that reaches a server we run is a bug report or feature request you choose to send from the app. What that carries is set out below.
The app does talk to other services — to find a poster, to look up a description, or because you asked it to connect to a tracker. This page says which, and what each one sees.