Shame Project Fi is so badly overpriced in the first place and limited to almost no choice of hardware. I pay $40/line for unlimited voice, texts and data with T-Mobile, with the only catch being that streaming video is throttled to bandwidth sufficient for a 480p feed. With Project Fi, that'd get me a paltry 2GB of data per line before I was paying more than I am now for T-Mobile.
I just checked my usage, and on my phone I'm using 2.9GB/month currently, while my tablet is using 9.7GB/month. (And that's for cellular data only, Wi-Fi not included.) Can't check my other two lines right this second, but even if we pretend that they're not using any data at all, I'd already be paying an extra $50/month for Project Fi over my current plan, which allows me to choose my own device (I bought mine retail from Asia using Expansys), and which is fast and reliable almost everywhere I go (literally the only place it has been spotty for me was Austin, Texas, but my friends on other carriers were all complaining about their coverage there too.)
You couldn't persuade me to switch to Project Fi if you tried.