Me personally, I enjoy having books like UA lying around. Comes in handy for making adjudications sometimes. I use it as a "secret" GM mechanics system sometimes.
As for facing, it is one of my favorite. As a practitioner of combat irl I love the realism it introduces into a game that was based on a tabletop strategy game anyway. I was sad that we forgot, through the editions, where it had come from. Too often I have players take advantage of 360 degree awareness. As I like to be visceral with descriptions and they tend to interpret every word I say literally in game mechanics terms, it's become quite the lifesaver.
So overall the book for me is prophetic. My players would have me burned at the stake if they knew I said that. So lets keep this little secret between us...