Hi, I think it"s a capacity thing, at least do People say so in other forum, Google and You will get plenty of results on for exampel Sailnet or Cruisers Forum.
That said, we love our NH. We can stay in a place for weeks with no ned to go to a pumpout or destroy the water around us. The urinetank i easy to empty on land or in the sea, depends on were we are. We had one NH on our earlier yacht to and switched in our new as fast as we Could. We sail in the Baltic, mostly Stockholm arkipelago.