Yes, I've been using Google Fi for a while now. About 6 months or so. They gave me a big credit when I signed up and I didn't have to pay for like the first three months. Now I pay a little less than what I was on an ATT prepaid plan. I use more data in the winter when I'm out at the track, should pay a little less in the summer. The thing I like is my cell coverage at work was pretty bad, now with Google Fi it will use the wifi for calls so it is not an issue.
I don't really use that much data so I can't say. You get free data for anything over 6gb but I don't think I've ever gone over 4gb in a month, even with really heavy use for me. I normally stay under 3gb.