What cell service is perfect? Fi is wonderful for a simple pricing structure and having service in 170+ countries as soon as you land. It allows me to use my phone in the few hours it takes from landing in a new country, to getting to my hotel, to getting to a cell provider to get a local SIM.
It is only officially supported on Nexus and Pixel phones, which are great devices. You can get around the limitation by doing some Googling as well if you insist on using a different device.
"By no means perfect" doesn't mean "isn't perfect", it means "it's actually quite a long way away from being perfect".
I check in on the state of Fi every so often, and from what a lot of users are saying about it, it seems to be at best beta quality, and that's using the handful of officially supported devices. Perhaps in the countries you've been to with the device you use it's fine, but it doesn't seem anywhere near as reliable as picking up a local SIM.
Throw in the fact that it's not officially supported for most devices and that it's only available in the USA makes it a complete non-starter for me.
Also:
> if you insist on using a different device.
Having a device that Fi doesn't support isn't me being unreasonably stubborn like you seem to think. If Fi doesn't support the device that I use, that's Fi's shortcoming, not my own.
Once Google Fi is activated, it can work on iPhones and other devices. I use it all the time when traveling. Data-only SIM cards are free on Fi, (with no monthly recurring fee) so you can roam on multiple devices and only pay a very low fee ($10/gig) for what you use.
?? I thought Project FI had a min $20 a month basic rate. Looking at the site it certainly looks that way. Is there a way to have a Project FI account and no monthly fee if not used?