I'm not saying go out and buy one of these as there looks like loads of excellent mk5 suited HU's now, but I can only go off my own experience and compared to the RCD300, well there's nothing to compare. Even compared to the previous Zenec model I had this one is streets ahead.
I have a Kenwood TS-WX77A flat sub and all of a sudden it actually sounds a bit punchy as this model allows you to tweak the audio more than just a rock/pop/classic type equaliser. To be honest this is as far as my audio skills go, so sorry I can't help more on that!
As for the satnav, well yes you can pay for updates for the pretty good Igo8, or you can get maps from other places...I have the up to date PocketGPSworld cameras as I have a subscription.
Yeh it doesn't matter where you purchase, worst case scenario you have to change the language (if you do buy used make sure it comes with the PIN code if they have changed it from default).
Some NC2010 pics for you guys with questions...
Hope this helps?