Meross has anyone tested its watt readings ?

[MasterCATZ]

I bought some meross smartplugs (MSS310AU)
because I wanted some power monitoring on 3d printers and aquarium air pumps

no matter what I have tested I always have it reporting half the wattage that is being used ?

300watts pumps are showing 150watts
160watt pumps showing 80 watts
1.5kw computer showing 750watts
300watt 3d printer 150watts
even using an inverter running only 1 device is also 50% variation to what it is saying its outputting  ...

they are saying no one else is having any issues and that it might be because I am not running Incandescent lamps etc ...

my current clamp metre / other watt meters are matching up ?