RNS-E/RNS-D Advice please

Am looking to get a sat nav fitted in my A4 but not sure what option to take. My choices are between the RNS-E which seems to be about £400 vs RNS-D about £250-350 both with price on top to have the fitting and setup done and aftermarket double DIN about £420 that seems to have more features.

I see everyone saying how great the RNS sat navs are but i cant really find a lot that describes what features they have. Ive gathered that the difference bwteen the RNS-D vs E is that the E is DVD map based and has an SD Slot for music and has a bigger screen vs the D model. You cant use the unit to play DVD's without an external device. But it shows something? on the DIS for satnav where the aftermarket ones dont.

Aftermarket ones have DVD/MP3 capability and bluetooth. Play music in satnav mode.


My question is does the RNS-D support MP3 playback on disc and does it have an SD reader like the E?
Does the D/E units let you play music while in satnav mode?
Is there any other differences between the D and E models that is worth knowing.

Not really sure what to decide on and hoping someone can shed me some light. Want to make the right decision when it is going to cost a fair bit whichever route i choose.

Cheers
Daz

i see. that clears a few things up. seems that the E is worth the extra money over the price of the D model then.

What is the nav unit like compared to say Tomtom units to use are they any good, touchscreen etc.

Another query, i noticed on ebay like a small satnav remote. seems to fit in the little space behind the cigarette lighter. What is this for/what does it do and is it a pig to fit in?

cheers