Consider yourself to be very lucky, I dropped Fi when the protection plan for my Nexus 5X which had a swelling battery after less than two years only offered a cheap "Motorola" phone that among other thing was reported to have bad WiFi performance, negating one of the big advantages of Fi.
Here, as long as this refurbished replacement is the same device, and the warranty either continues, or if needed gets extended by at least a couple of months, you should be OK. Many returns have absolutely nothing wrong with them, or something really minor.
If Apple's iOS software quality wasn't awful and getting worse, I'd recommend checking out iPhones, I just had a very good experience getting a problem fixed at my local Best Buy. But having to be concerned that software updates will take out your phone, or WiFi, or other basic functionality means this will be my last as well as first iPhone.