ESP8266 Plug is a small USB to serial bridge intended to ease debugging of ESP8266 WiFi serial transceiver. Using your computer’s USB for serial port emulation will definitely make debugging easier than doing first time discovery with microcontroller.
Since usual solution of just abusing FTDI cable cannot really supply this module with enough current once things get going, there is a separate 3.3 V voltage regulator for all the peaks ESP needs.
Additionally there are two special solder bridges on the bottom. One for putting ESP8266 module into bootloader mode so it can be revived in cases of bad firmware updates. Another bridge controls bootloader via DTR signal line - useful for automation.
Whole device is quite small in size and easy to assemble for anyone with SMD soldering skills.
Thanks for information.
ESP8266 have 3 modes , boot from SD card , Boot from Flash and Boot from UART.
