I'm always looking for a good deal... I'm not so sure this is one.
A comparison with my current plan... I have 4 phones, each with unlimited talk, text, and 5gb data for each phone. My monthly bill is $149
Google Fi = Must purchase one of their phones, only two phone options. $200/$350 each.
My Plan = Bring your own GSM phone. Sim cards cost $10.
Google Fi = Unlimited talk and Text $20 data @ $10/GB. Total cost for unlimited +5GB = $70
My plan = Unlimited talk, text, and 5GB data = $35
Google Fi = Sprint, T-Mobile, and U.S. Cellular, 4g lte (roaming talk text and data)
My plan = T-mobile 4g lte ( roaming talk and text, single carrier data)
So the Google Fi plan costs double what I'm currently paying, plus a minimum of $800 to purchase 4 new phones. All this to get the benefit of roaming data.
No advantage for me... but YMMV