You're right it's comes up on Carousel.sg here
https://www.carousell.sg/p/joy-7307-multifunction-calibrator-1007081430/That even has a what's app number to chat to the seller. If you look at his other items he has that 6.5 digit multimeter plus a load of advantest 8.5 digit meters for sale. This looks like the developer.
Google translate gives this slightly more detailed spec from the carousel page.
Features
MEAS:
DC voltage measurement, range 0-12.5v, resolution 7.5 bits, INL<1ppm after compensation, default filter mode.
DCV:
10V file, adjustable range -10uv~11v, resolution 7.5 bits, INL<1ppm, Tc<0.3ppm
1V file, adjustable range 0uv~1.1v, resolution 7.5 bits, INL<1ppm, Tc<1ppm
DCI:
100mA gear: adjustable range 0~110mA, resolution 6.5 digits, INL<10ppm, Tc<3ppm
1mA gear: adjustable range 0~1.1mA, resolution 6.5 digits, INL<10ppm, Tc<2ppm
Ω:
Fixed physical resistance output, a total of 9 levels: 0R, 10R, 100R, 1k, 10k, 100k, 1M, 10M, 100M. Each index is related to the resistance performance used. The calibration value is 7.5 digits display.
Power: Power on/off button, long press for 2 seconds to turn on, then long press for 2 seconds to turn off
Meas: DC measurement mode
Dc.V: DC voltage output mode, use shift+up and down keys to switch gears
Dc.I: DC current output mode, use shift+up and down keys to switch gears
Ω: physical resistance output mode, directly use the up and down keys to switch gears
TC: No function
G.NULL: Guard switch. shift+null is the measurement mode return to 0
EXIT.B: Menu exit key. Shift+B turns on and off Bluetooth
SHFIT: Multi-function key
M.AUTO: Menu. Shift+auto is automatic range conversion
<: cursor to the left
>: cursor to the right
︿: number increase
﹀: the number decreases
OK.OUT: Menu confirmation key. Shfit+OUT, output on and off