We just initiated a Google FI account for my wife and bought one of the Nexus 5X phones for $249 (the $199 16GB was sold out). I think the best feature, often overlooked, is the ability to get a second data-only SIM. We put the SIM in my I-Phone and it performed flawlessly with my free Google Voice/Hangouts service. But, because with Project FI you pay for each GB of data used, it is in your best interest to minimize the use of cellular data, which is difficult coming off an unlimited, company paid plan. But, we figured we could use the extra data SIM to create a second phone and our pre-tax cost would be around $30-$35 per month for what amounts to two cell phones.
***As a bonus, I took the data SIM to Hong Kong and, without extra charges beyond the normal data usage rate, used the data and Google Voice functionality and both worked great. I'm sold, I still have a company paid phone; but, when/if that stops we will use the single Project FI account with a data SIM/Google Voice as our two phone solution