I use Fi on a 5X in the Cincinnati area, and I am largely satisfied. Observed opportunity: Fi seems to select the network based on the relative strength of the LTE connection. In my experience, data over LTE is adequately strong on any available network in my area, but voice service is distinguished. Tmo is fine but Sprint is weak. In particular, my phone falls to Sprint at my home, where the voice connection is very poor...hang up, airplane mode, call them back over WiFi poor. If my calls were executed VoLTE, this would be solved. If a widget enabled me to lock to Tmo, this could be solved. I use SignalSpy to temporarily designate Tmo, but it falls back to Sprint in time. All-in-all, I survive but less techie users would give up and switch service.