I have the Nexus 5x and have had Google Fi for about 6 weeks or so. I too live in an area where the only good cell coverage is through Verizon.
The two minuses I have discovered are the battery life on the phone and crappy call quality when trying to participate in a teleconference from home (I am guessing it was trying to use WiFi). If I leave the phone on all the time I will need to charge it almost every day. With the teleconference, the sound quality was poor and the call was dropped after a few minutes. Luckily for me I have alternatives, so not a real big deal for me, but if this would be your only phone and you live in a spotty cell coverage area, something to consider.
I can’t complain about the price, for sure, I like only paying for the data I use. This month’s bill was only $23. And I like everything else about the phone itself.