Difficult question and old question.
In the last years helicopters and their equipment was very improved. Much more than on the decades before. The use of NVG, GPS, FADEC, Autopilot (now better "Flightdirectors") gives the pilot much more possibilities to make the flight successful and safe. The older times with the chart on the leg, trying to spot the location in the small white or red lights of the instruments
and flying the ship only by hand are gone. Shure we have a lot of ships without autopilot, but GPS (mostly with moving maps) should be standard today. One pilot is today able to fly the ship nearly under all circumstances alone. The second pilot is mostly a "controller" and the use of Crew Resource Management should give a advantage in safety. But no one can really count the CRM advantage. Most examples of the CRM guys coming from planks. They haven't great experience in helos and mostly they couldn't imagine the kind of missions a helicopter have to fly. And a lot of accidents, are crew misunderstanding accidents. I think a second pilot couldn't hurt but isn't necessary under all circumstances. With a 50 years history helicopter operations are proved.
Keep it simple...
I hate all the statistics comparing singles and twins. You could find any possible messages, if you like, in statistics. Look at
AMPA Safety Report.
Single or twin, it's a question of the kind and the circumstances of your mission.