Could a harness possibly add risk if the aircraft is in a ditching situation or a fire? I think we would need to analyze that carefully.
In an apparent autorotation and ditching it appears the pilot escaped safely unfortunately everyone else is left stuck inside the capsized aircraft, rescuers did not arrive in time.
These open door experience flights are becoming very popular, obviously if people are flying with the doors open they need to be harnessed, the only downsize to a harness is they are can tough to remove. They were not using regular seatbelts, Flynyon uses skydiving type harnesses that are very difficult to remove, and when you are panicking removing a complex harness is much more difficult. Now one could argue even if they were not harnessed they still would have had difficulty escaping, since the aircraft capsized, but their chance would probably have been higher, especially considering the doors are open allowing easy access out. Also, Offshore workers are trained in HUET (Helicopter underwater emergency training), tourists are not. For the sake of the victims I would like to keep this discussion about safety and not let this descend into a free for all bashing opportunity, which is unproductive and disrespectful.
Here's a video showing HUET training, notice the seat belts are quite easy to remove, rescuers at the NY accident said that they had to cut the harnesses.