Earlier quoted context omitted.
While technically true "the US" here is only used as an example, I don't believe the endpoints have to be in the US (if I understand correctly any user of this extension can choose to become a proxy). An other point in the video (at around 0:50) mentions that you can select your route through trusted friends. If that's true it means that you can decide where your traffic transits. Now obviously if you use the binary…
If you don't trust Google, run it in Firefox.
if you don't trust Google...
you probably shouldn't run it.
As it is pretty difficult to run reliable audits these days... I would not run it. You open yourself up to everything from the American Homeland Security people to Child Pornographers.
It's just not worth it.