Sure, I give Google the benefit of the doubt in regard to user data collection on GF. As for caching, mobile phones have very small caches and will reload font

Sure, I give Google the benefit of the doubt in regard to user data collection on GF. As for caching, mobile phones have very small caches and will reload fonts frequently, specially with the large variety of fonts available. And if the browser can cache font files it can also cache stylesheets with base64 encoded fonts, saving requests at the same time.