It does have partial postcode search, e.g. you could enter RG31 5 and it would then give you a choice of roads within that postcode area.
Certainly does have audio directions, which are easy to understand and follow, and a button to replay the instructions if you missed them. It can also be set to display the current road you are on even if you have not plugged in a route (which I find very useful sometimes)
Arrows etc for directions are displayed both on the colour screen, and also on the screen between the speedo and rev counter.
No doubt that an aftermarket version is cheaper but it will never be completely integrated