Being the only knowledgeable person in reach, I was asked by this lady to reset this phone after the owner forgot its password. It's an unnamed model apparently powered by a Spreadtrum SoC and built to imitate the LG G4. Judging by the lockscreen blocked by a Google account password prompt, it seems to run on Android 4.x.
Power + Volume down lands on the screen on the left, which contains just generic test routines.
Power + Volume up gets you into what seems to be the fastboot mode. I'm planning on attempting to flash generic recoveries but I'm slightly wary of USB connecting it to my mission-critical notebook. Either way, I wouldn't know which recovery to flash or, if it comes to, which ROM to flash in it.
Ironically, this might as well be the most secure device I've touched.