I've got a 2DIn satNav unit. I've a chinese unit and I'm satisfied.
I took the original HU and got a surrounding like the one on the post #1.
As to the GPS antenna I put it in the dash board in front of the Day/night sensor and I didn't have any problems with the wire because it fall easillybehund the dash board. Just dismantled some plastics next to the door so that the wire could pass throught the glove compartment into the HU hole.
The most difficult part was the reversing camera but I manage to send the wires next to the original cables through the chassi next to the doors into the boot.
As to the aerial, as it is an active unit (it needs 12Volts), I had to buy an inserter.
The original cabling and sockets remained untouched and I made the conversion (New unit cables / female original socket).
The unit can run any kind of navigation software. I've got a 4Gb SD card with IGo 8.3, TomTom, NDrive with the maps of Portugal, Spain and Gibraltar.
I can always make phone calls because it has got bluetooth; listen to my favourite iPod music selection, watch the telly or a movie; it also has got USB front connection and AUX (video and audio) input.
There is the possibility of still using the steering controls but it needs an adaptor.
If I can I'll put some photos of the THING

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PS: Although it's a Chinese thing it worths the money €275.