In reply to Neo.

By self-hosting these fonts it’s possible you’ll miss out on ongoing improvements that are automatically delivered when using the Google Fonts API. It’s still preferable to self-host but it may be a better idea to download fonts directly from Google Fonts, to at least ensure the font is the most recent release. The webfont-helper-tool appears to offer slightly different versions (based on differences in file sizes I’ve observed) but it’s not obvious why. Interested whether anyone can shed some light on this.