pbilling :
We have been on Fi just over a year now and love it. Very sketchy cell service in our house and none in the basement. With Fi and wifi we get coverage everyplace at home. Out and about the service is on par with what we were getting from Verizon and much better then our friends get with ATT. Good article, but almost no mention of the fact that Fi uses WiFi for calling, for us this was the biggest benefit.
Wifi calling worked sometimes, but mostly not for me. While Wifi calling works well on my iPhone on Verizon *sigh*, the Project Fi version was mostly prevented from working by having low-level Sprint coverage. And the mode for calling is "Cellular preferred", which means if there's any cellular coverage, use that. Our Sprint coverage was variable but enough for Fi to attempt to use it, no T-Mobile coverage, but enough Sprint coverage to inhibit wifi calling. Glad that it worked for you, though! Be aware that it may not work for others.
It is low-cost to try, though, if you already have a Google phone, or Moto X4 in Android One mode. Or would have a Google phone anyways.