I spent quite literally half the last year outside of the US and suffered no such penalty. I have their unlimited plan and everything worked just fine. I don't make many calls, but when I do if you're outside of US/MX/CAN you can do so over wifi for free and my data worked fine.
Most of my time was in South America, I can't speak for overseas if this is the same.
I have never really had complaints about Google-Fi.