well, thank you very much Yenzehn for your quick input !
The device comes actually with USB cable and microSD slot so I hope there must be a way (using either USB or SD) for someone to re-flash an earlier Android version or a newer version ?
I've played around with it for over 1 hour, played with all the settings, clicked everywhere 1,000's of times, that thing in red "Demo Purpose Only" is still there in the top left corner ...
I've sent an email to the eBay seller in Hong Kong asking them if they know a way to get rid of the message, waiting for them to get back to me. Otherwise everything else seems to be working OK, WiFi and everything, ok there's an issue with the AppStore (it's not the Android Market one) and has fewer apps and many are in Chinese too. But I guess I can always pass some free apps (some games I like, etc) through the USB or the SD method as raw ".apk" files, no ? (haven't tried this yet)
But if finally there's really NO way to get rid of that red message I will return it, I won't tolerate this anymore, that message really drives me mad ...
Any other suggestions anybody guys ??