Hey!
It's a little tricky. Officially we don't really have a 1.0 release, but that's mainly because we keep adding features to the list of things we want before we officially release v1.
As the note on Github says, nothing is 100% perfect. Occasionally, bugs will come up. We haven't had a third party security audit of the app yet either. But even with an audit, things are missed - The NSA kept Eternal Blue under wraps for ~5 years before it was patched. Note that under the terms of the GNU GPL, there is absolutely no warranty, etc (we do offer private donstor support if you need an extra hand).
All that said, we have quite a few MSPs using this in production (including @johnny). I'd be quite comfortable putting customer data in ITFlow at this point. It's ultimately down to your risk appetite.