[gst]

With Google Voice I have a phone number not tied to a particular SIM card or to a particular phone. When I travel internationally I can use a cheap local SIM and I'm still reachable on my US number for calls and texts.

With Fi you run into issues if you use it for too long outside the US. And also I read that people had troubles re-activating a Fi eSIM from outside the US in cases where they (for example) lost their phone.