I want to jump to Fi but is just super expensive for families. I have 4 lines.
With Mint I can get unlimited talk, text and 2GB/per line for $15. So a family of 4 = $60.
With Fi it would be $145. The difference is more than double.
ATT offers 4 lines for $120 with 3GB per line.
I remember when it was launched the price advantage was big. But since then the carriers came down and Fi did not (barring that $15 vs $20 per extra line thing)
The only advantage I see is the use of 3 networks(for those who live in places with bad coverage).