At 5.53€ this is indeed a board comparable to the Arduino Mega, with a microUsb connector and can be powered by a lipo battery, even tough it lacks any logic of power management, except a 6-12v regulator.
Can provide 800mA at 5v adn 350mA at 3.3v.
This is an interesting board for robots, expendable sensor central to place outside or just an handy board to try the ATmega.
If you already tried the Nodemcu v1.0, you should be already in love with the version based on the ESP8266.
Anyway this board aims to deal with the limitations of the ESP, with 22GPIO pins instead of 10, and a slightly more powerful chip.
If you ever had the feeling that the microcontroller you are using is lacking on analog pins, this is a 3.50€ budget solution that will give you access to 4 deluxe 16bit resolution analog pins.
16bit resolution means results that go from 0 to 65536, and this chip can gather 860 samples per second, from 4 pin at the same time.
It has also a programmable voltage range, which means you can get all the precision in a narrow range of 0.256v or have a range of 6.144v.
It is friendly to use with all microcontrollers that can use I2C, and can also signal when data is ready, can be reconfigured on the fly, and drinks 0.15mA at full use.