MATT YSBK,
Have to agree with Centaurus entirely concerning UA's overwater with no horizon at night! I think the risks far outweight the advantages in this case; especially in a helicopter which is inherently unstable and incredibly unforgiving in certain flight regimes - mast bumping is one phenonema I would not even like to consider in such an exercise! Some people appear to forget that it is a NVFR rating and to convince people that they can do more than that through minimal exposure to those conditions could be quite dangerous!
It is generally when pilots take their aircraft outside the scope and strict limits of the rating that they find themselves in trouble and for the most part, this falls back squarely to sensible, realistic training with clear advice to pilots about the limits of the rating.
I stress those limits to my trainees and advise them in the first briefing that the rating is really designed to finish a flight after dark when the weather permits or conversely, to commence a flight before first light in good conditions. For that reason, their first navex is commenced before last light so the candidate can experience the transition into darkness.
Capn Bloggs, Feel free to pop down anytime for a night auto's serial - it's no more dangerous than driving through Redfern at 2am with the windows down!