The big thing keeping me from switching from Google Fi is how easy international roaming is. For every country I've been to, I've just had it automatically work within ten minutes of landing, at my regular price, without buying any addons
Except if you happen to travel for more than 45 days, in which case Google Fi will promptly tell you to get fucked and cut off your service without warning, advanced notice, or spelling out anywhere when you sign up. Not my idea of a carrier I can trust. I deleted my account and service with them to move to a carrier that I can trust and actually respects me as a customer.
tbf, that was because a lot of people abused it by being permanently outside of the US and relying exclusively on the roaming for all their data. I know because I was one of those people for 6 years.
I got bad speed even with perfect signal in malls and any place that is more crowded than a Costco. Google Fi doesn't have that problem. I blame it on T-mobile but I would rather Google Fi survives.