A brief refresher: Project Fi is Google’s attempt to provide the be-all-end-all for your smartphone needs. It’s a mobile virtual network operator, or MVNO, that switches between T-Mobile, Sprint, and Wi-Fi intelligently so that you have the best service between the three
Bleh, Tmobile and Sprint, I wonder if that's why it's so cheap. I've had issues with both of them.
And wi-fi. Google is mapping public no-PW-req wi-fi hotspots for seamless switching. For me, I have good wi-fi available 90%+ of the time. Fi is no contract service, so you can take your Nexus phone elsewhere at any time if you're not happy.