Also, Google Fi kinda sucks. They used to be the cheapest, but nowadays you can get better prices from other services. For example, Google charges $10/gb/mo, whereas Mint Mobile (another T-mobile MVNO) charges 4gb for $15/mo, or $30 for unlimited.
Google Fi is only cheaper if you use less than 1.5gb of data per month, and the service quality is probably the same.
...and that's not even mentioning all the privacy concerns attached to Google.