I got mine through Fi and have been using it for about a week. So far it’s great, I haven’t had a single issue. I previously had T-Mobile so I knew my coverage would be fine. My coverage has actually gotten better which was a pleasant surprise. Since they use both T-Mobile and Sprint I’m now pulling an LTE signal in a few places on my drive home from work where T-Mobile would bounce me to H or 3G.
I’m in the Boulder, CO area so my coverage is pretty good. I doubt I would do Fi if I spent most of my time in a rural area. With that said I have a long drive to Dallas, TX next week and I’m looking forward to seeing how well it does pulling a signal out in the boonies.