I have a birdview so I have no issues with the unit. Its great for general driving.
Downside, it doesnt take postcodes and you cant update it. New disks are released every few years but cost several hundread pounds.
The unit new costs about £1300 from the dealer plus 5 hours fitting so close to £1800 installed.
You may be lucky to get one second hand but to be honest, and in my view only, you can get a fantastic multimedia system for a lot less.
Several owner have retro-fitted great systems to their cars. Have a look through the ICE section.
Welcome to the forum by the way, stick a post up in the intro section so we can all say Hi