Dick Smith what was so fatally flawed about NAS? ... the maximum use of radar is ensured.....
The biggest problem is that in the US where it was developed, they have something like 80 to 90% radar coverage and can actually see all those VFR flights that are not required to submit details.
Here in Australia we have about 15% of the geography covered by radar - and even that relies on transponders, so won't pick up the little guys without one.