It seems okay to me for the case of google. Since Google-owned sites, Adsense, Gmail, and Google Analytics are so ubiquitous, things like a font download are trivially easy for Google to correlate to your other activity. There's much less value for BunnyCDN to abuse it, because they don't have the critical mass of your other activity.
Yes, just serving up your own fonts is better, but this is an improvement that seems to work with only a minor change.