Yeah my bet is on laser.
Is it possible to just paint back of the panel and then use laser to burn it out, then apply different color(layer), then burn again and again?
Also what's the downside compared to proper $2000 6 1/2 bench multimeter(apart from max 100V)?
There are a few extra limitation compared to proper meters.
The INL if those SD ADCs is not that great. Besides the ADC the cheap resistors can add to this.
Only small ranges (if at all) have high impedance. So not > 10 GOhms for a 10 V range.
Due to the cheap resistors used the drift / accuracy are likely more like at the low end 5 digit level.
The possibilities for a proper calibration may be limited.
It looks like there is no Isolation from the inputs to the display and maybe even interface (if there is one). Having a PC interface (like GPIB) can be an important factor.
However there are also a few up's: the SD ADC can read rather fast and has low noise. There is also internal anti aliasing filtering. So used as a digitizer at something like 1 kSPS this can be rather good.