Heard a few people say that they sound different but unless your one of them audiophiles (and i know there is a few on here before you shout at me) the RCD sounds fine to me.
However i'll be getting an RNS soon, who did you get yours from Scott? 
I would think anyone who's really into their music would be going after market though. Sure, it may not look as nice and go as well with the interior, but it would sound better.
I bought it off eBay mate, it's version H (latest version at the time - probably still is) and think I paid £600 delivered.