The pay as you go usage was really good. I really only used my data in Delaware. I often ended up about 30$ a month or so. There were a couple of occasions where it would If it weren't for the call quality I would have stayed but...
I had heard some complaints about call reception for Nexus 5X. I didn't get to try it on another carrier. My phone was knocked out of my hand at a bus stop, and the screen cracked. I would say go for it. There are good promotions for the Nexus phones if you need one with project fi activation.
I was a bit worried that the "pay for actual usage" bit would make me be a bit more frugal about my phone use, but it hasn't turned out that way.