I have been using Google Fi for over two months now. Sadly for me, I am out in the countryside, so I do not get near the speeds that I am showing with the screenshots. That is unfortunate because I would be quite happy with them.
My speeds are 1 percent of these speeds I got. I am just in a bad reception area that allows 4G and 4G+ if I walk up a hill. Still, getting these speeds in town shows that Google Fi has good speeds once you find them.
If things work out right, I will move to another city in the US. Then I can get some great speeds.