I've had Republic for about 2 years now. I have a dedicated Verizon voice-only flip phone that I also carry.
The Defy XT is a slow phone, runs an old Android, and has very limited memory. The newer phones should be better, but the plans become more expensive. I pay $19/month for unlimited everything.
In the Boston metropolis, Sprint is great, but once you head into the rest of New England, good luck getting a signal. It feels like unreliable dial-up in many places, and don't even dream of receiving a call when the service is spotty like that.
For me, it's a "nice-to-have" internet device, but not a primary cell phone.