Hi Ella's mum,
Not only did I never get a +ve OPK, but I barely even got a second line including the cycle I fell pregnant. I followed the instructions very carefully, sometimes testing several times a day, but did not seem to find these tests useful for me. The only way I could ever actually identify if/when I ovualted was by getting my blood checked to see if I had ovulated.
Good luck - your faint lines sound promising.