I just drove my NX to So. Jersey from CT on Saturday via the Garden State & NJ Turnpike. Normal NJ driving gave the pre-collision system plenty of exercise ... it hit the brakes several times. But, given that environment, I would not recommend it. There were a few times where drivers behind me were clearly surprised by the abrupt slow downs the system made. Nothing beat real defensive driving in expecting the unexpected. The drivers behind me clearly had no concept of watching drivers ahead of me either.
As it was my 1st real test of the system, I let it run at the default detection distance. On the way back I reduced to the mid distance and seemed slightly less eventful to the rear even tho the gap between myself & the car in front became slightly more eventful.
There were a few other little anomalies such as across 3 lanes of traffic with slower cars in the center. The system picks up on the slower cars which could make you a hazard for the faster moving cars in the lane you are moving to. Sounds obvious I know, but the slow down can be quite abrupt.
Conclusion is that I think it is a very good feature, but requires an adjustment to driving technique.