I bought this ruler after a friend loaned me her's for a "test run", and being impressed with the ease of use and the precision achieved using it. I use it mainly for squaring up my blocks and it has quickly become one of my very favourite rulers.
It would have served me better with cutting slots going in both directions. I have to turn and re-align it after every side cut. Otherwise, it's a help to cutting straight. I like that the direction lines are clear and I can mark the surface with a felt tip pen to easily reproduce identically-sized squares.