I've been using it for about a year, and got it exclusively for international use. In sort, it's excellent.
ATT and Verizon's international data roaming plans are awful. You get some combination of:
1) Roaming on the crappy old networks, e.g. 3G or even Edge/2G instead of 4G/LTE
2) Very limited data before you get put into some sort of limp mode at sub-dialup speeds.
3) Very expensive/limited data plan roaming on the good networks.
I got the FI phone before heading to Mexico this time last year to use primarily for data, but also for voice. It was as a replacement for a Verizon USB modem that I have, and an ATT mifi hotspot. My purchase was 100% driven by international data roaming capabilities and services.
The Google FI device is vastly superior in pretty much all ways. The base plan is $20/ month, so low cost to carry when not in active use. Then you pay $0.20/min for international roaming calls, which I can live with. You pay for data up to I think 6GB, then the next 6GB is no extra charge. Above that they might throttle you, but you also have the option to buy more. I never exceeded 12GB even though it was the primary data for our whole boat and everything on it. I set it up as a hotspot (no extra charge), and connected the boat's wifi extender to it, just as you would connect to a marina's wifi.
Throughout Mexico, I got better data service though the google phone than through any marina. Now you might say "oh, but it's Mexico", but I found the same true in the US as well. I think I could count on one hand the number of marina's is the last 4 years with usable wifi.
In the past month or two I have spent over 3 weeks in Europe, and used the Google FI phone there as well with no issues. This most recent trip, I tried something different, and didn't set up any international plan for my phone or iPad. Normally I set up a de minimis plan for each as a back up. Instead, I connected my phone and iPad to the Google phone hotspot, and used ATT wifi calling through the google phone. It worked great, and saved me between $60 and $120 for the crappy international plans on my phone and iPad that I usually get.
Worth noting is that when the phone is acting as a hotspot, it can't also be connected to a wifi service, so 100% of my communications was via LTE data service, even my "wifi calling" phone calls from my usual phone. Someone speculated that it uses wifi whenever possible and does wifi calling. It might try, but I have never seen it connected to a wifi access point that I haven't explicitly enabled. So it's certainly not a dependency for the service.
I'm off to Asia soon for a week and will see how it works there too.
The down side from my perspective is that it only works on select Android phones. I hadn't used one before, and oh my god what a confused and inconsistent splatter of functionality those phones are. But I've powered through.
And related to that, I got a note from Google just today saying that they would be supporting a broader range of phones including iPhones, but with certain reduced capabilities. I don't know what those reduced capabilities are, but will be checking it out and might move my primary service to them at some point.
