It does need it to work right in the US (Neo19's manual shows no iso, so I assume they work okay in Japan). I fought for YEARS with weird issues with mine in my Neo19. Even went so far as to get a second chassis, then a third chassis, still the same weird issues, take the monitor to another house to make sure it wasn't my wall power, same issues. Only thing that resolved it was an ISO transformer (in my case I just used a spare stepdown but it has the same effect).
You won't blow it by plugging it in without one, but you will have all manner of strange issues pop up that you'll never be able to track down.