Well, he's only been there a week. That doesn't tell you he's safe. You must consider that 4 riders have been injured by him. Did they all ride the same? Did they know each other? Did he live at the same place for those intervening years or was he moved around? How many people regularly rode him? Do you know the circumstances of the injuries? Give it time and be on your toes. As nice as he has been so far, it takes months for a horse to adapt to a new environment and behaviors will change over that time.
On the other hand, he may be a one person horse. They do exist.