This Smart Plug actually contains the ubiquitous ESP8266
Theo Arends has already done much of the teardown work here
Rather than burning the Sonoff firmware, I have chosen to use MicroPython to make a Home Assistant compatible smart plug.
The plug uses MQTT to talk to Home Assistant, and includes the ability to set or change the wifi credential at any time. You can also run the MicroPython REPL over the wifi. So, once you have loaded MicroPython, you will never have to open the plug again.
See full instructions on my GitHub at https://github.com/arendst/Sonoff-Tasmota/wiki/Hyleton-313-Smart-Plug.