Can an OBD2 HUD Display drain car battery?

[Mastro]

I purchased an OBD2 Hud Up Display for my Aygo (2006). Great reviews overall.

Manufacturer claims it uses 400mA when in use, and, what I care about; 0.3mAh when in Sleep Mode.

It goes in Sleep Mode when ignition is off. Now I know 0.3 is almost nothing, but I have a hard time believing it's THAT low. Not exactly saying manufacturer is not being honest but, 0.3mAh?

I also contacted them and they told me it's better to unplug it if I DON'T drive the vehicle for 1 week+. So if it's indeed 0.3mAh, why would they advise me to unplug it after a week when in theory it would take months, or years to completely drain a car Battery at 0.3mAh?

What is your experience with OBD2 devices? Should I be worried to leave the device plugged in?

I mean I can always test it and have a nice jump start the next day, but I don't really fancy that lol. Plus I don't think it's good for the Battery itself.