I've been happy with Google Fi for almost 2 years, but obviously I've been using one of the optimized Android models. I usually pay $25-$35 per month, depending on how much data I use. Billing is very straightforward. The data reception isn't great in rural areas, but it wouldn't be with Sprint or T-Mobile either.
About one year into service, my Nexus phone bootlooped itself, and I popped the Google Fi SIM card into an old iPhone model. I had no problems making and receiving calls or texts. LTE data worked on that phone and has always worked just fine on my iPad (if you have a Google Fi account, you can get a free linked data SIM card for a tablet and only pay for the data that you use).