Disclaimer: I only red the TLDR.
> I don't know if mine is an isolated instance
I would think so. I'm not even US citizen and used Google Fi in 10+ countries over the last year. With iPad and iPhone before iPhone was even officially supported. The only hassle I have sometimes is a wrongly set APN but beside that I have good speed with 3G/LTE basically everywhere I go. So I wouldn't say Google Fi if fked per sè :)