Reporting back on the NH experience and comparison to SQ: as mentioned in the OP, flight itinerary was Saigon to JFK via HND. First leg in NH 787 - solids product, and generally great for a 6 hour flight, which I mostly spent sleeping.
Upon arrival at HND it became obvious that Japan is still in full lockdown mode. About half the passengers on the plane were transiting in HND (mostly to JFK). Before even reaching the main terminal we were held up by airport reps in the jet bridge, filling out all sorts of paperwork and making sure that no one could “escape” and roam through the terminal. After 10 minutes of collective confusion we were then escorted into the transit area, i.e. security check that ultimately leads back to the departure terminal. Fairly bizarre. Here the next surprise: with the exception of one duty free store all other shops are still closed - which only leaves the NH lounge as an option for the 4 hour layover. Lounge was vast, plenty of seating. Food options limited, though (COVID related?), and in a rather amusing episode I was asked to move into a phone booth area when I dared to take a call in the main area of the lounge. But fair enough, I suppose it serves the general ambiance which was mellow. Considered taking a shower but wait time was estimated to be 2.5 hours, so I can’t comment on the shower facilities.
The flight itself departed on time, something I always appreciate about NH - they just operate like clockwork. Now, for the “Room” cabin itself - it’s a great layout, and the space is huge for business class. Took a quick glance at first class, insane. It’s basically the Room x 2, with a gigantic screen. What bothered me, though, was the firmness of the seat. SQ’s seats are leather and fairly soft. 18 hours no issues whatsoever. With the Room seat - different story. After just a couple of hours I had difficulties finding a position that was comfortable enough for my lower back. Have others had the same experience?
Service is forthcoming and very kind, but the language barrier leads to a sub-optimal experience that requires constantly pointing out menu items. Depends heavily on the flight crew, though - I’ve had NH flights with flight attendants that would be fluent in English. Food absolutely outstanding and I agree with others’ views that the Japanese fare is more differentiated than SQ’s menu. That said, it took 3 hours to finish dinner, which is a long time as I was trying to go to bed to beat the jet lag.
In hindsight I’m very glad that I had the chance to fly both SQ on the way out, and NH on the way back. NH’s flight that was broken up into two segments made the journey significantly easier, and I loved the experience I had with both carriers. Service, IMO, better on SQ - each and every flight attendant is hustling and constantly checks in with you. NH much more by the books in that regard. In summary, one can’t go wrong with either product. NH up a slight notch over SQ in overall experience, but let’s face it these two carriers are deservedly among the top in the world when it comes to business class.
Thanks again for everyone’s inputs - happy to answer any specific questions.