I’ve had one for a while now and overall I’m happy with it. The screen and camera are as good as some other devices and it doesn’t support all of some bands that US providers use so service coverage may vary. I should also add that the touch sensitivity is a little off. I’m not sure if thats software or hardware to blame though.
I’m on a T-Mobile reseller and excluding situations like being inside a data center or being outside of town camping or whatever my service has been acceptable. Its also less an issue for me as in almost always in WiFi range.
I don’t think the phone is upgradable. It is repairable though. The fact that it has an easily removable battery is enough to justify the device for me as glued in dead batteries have historically been my biggest issue with device longevity.