I absolutely love the case for my iPhone, I have tested it in the shallows and it has shot some amazing footage. I believe the only let down for me is a small spot of scratches visible once opened from new right on the centre of the lense, resulting in a wee bit of blur in the photographs.
One other minor point, making no difference to the functionality of the case, is that sand seems to get stuck inside the springs in all of the buttons, making them less smooth to push. For the cases locking latch it is sometimes necessary to play around with the button to make it come back out and lock as sand can wedge it in the pressed position. This is generally fixed with a good rinse of fresh water.
I would definitely recommend putting some anti fog on the inside of the lense as well, sometimes after washing the sand out it will fog up even if it seems to be completely dry.
Ultimately, this is a very good case and I am excited to start taking it SCUBA diving with me from next week on.