I was truly astonished by this documentary.  It has the only footage I have seen of the inside of the World Trade Center on 9/11/01.  My wife absolutely refused to watch it, so I watched while she wasn't home.  But I am so glad I saw it.  It is the only human story of 9/11 I have seen that was actually filmed on that day.  There's plenty of footage out there of the plane impacts, people running in fear, etc. – but there is nothing else out there that really tells the story like this movie does.  It doesn't have anything truly shocking, so I don't think it is really dangerous to watch…but it is profound and it will stir up memories you may have thought were long forgotten.  Seriously, I do recommend this film.