It won't be utterly silent but it MAY be quiet.
I can't see it being any quieter than some of the larger non-reference cooled designs. Generally to make a heatsink smaller means that the fan is going to have to work harder so I would expect in terms of silence this is a step backwards and I never personally find graphics cards quiet enough unless they're passive or use a slow turning 120mm.
I do like to see a nice compact design though and possibly this is ideal for certain circumstances. I do wonder if the cooler would be ripe for a fan swap for something that doesn't spin quite so fast...