But seriously, it's basically a front end to a bunch of people who have been incentivized (or fooled) into installing a proxy server on their home computers. It's primarily of interest as a way to make certain types of fraud (like ad fraud and credit card fraud) much harder to detect.
https://lumtest.com/myip.json
https://lumtest.com/echo.json
It's powered by largest residential proxy network so they almost certainly never gonna ban your IP.