RNS510 cost-justified?

[Dubya]

What do owners of the RNS510 believe justifies its cost?

I may need to accept a car with RNS510 installed but will see if I can avoid it and have it swapped for an RCD510 if it is as overpriced as it appears to me to be.

On the other hand, I have never used SatNav in a car and so I am interested to hear the benefits of SatNav generally as well as how the $2,000+ price premium of the RNS510 over a premium portable device might be justified.

So I'd be grateful to those who might be able to share their experiences (such as when SatNav can be invaluable) and any other thoughts.

(I've read of the 30Gb HDD and DVD playback capability but on the downside I have also read that the RNS510 does not identify school zones and "safety" cameras.

I also know it is a "personal choice" and "options are optional" however what I am seeking is insights and experiences of people who have the device on board or the reasons people have decided to not check that box.)

Thanks in anticipation.