Ring is battery powered, with a battery life of 4 weeks.
It may not be obvious to someone not experienced in the design of battery-powered electronics, but that much battery life from a device with wifi and streaming video is very impressive - they must be making extremely good use of low-power sleep modes on their CPU, radio and camera.
Being battery powered means it can be self-installed, even by people who don't know a serial terminal from a screw terminal.
You can build something much, much better with about $100 with a Raspberry Pi, depending I guess on the camera quality. Are there any features unique to the Ring?
I am an advocate of using something like RPi's for Computer Science in Africa but I am a missionary without a following (thank goodness there isn't another crank like me going to central Africa).