Digital Outback Photo Sigma DP2M Field Report...
Interesting review. I notice there is a pictures showing that the Hoodman Hoodloupe works with it well. He notes it is good for bright light situations. I think others have reported the brighter view on the DP2,1 Merrill this may be less needed.
What I use it for with the older DP1 and DP2 we have is to get a more stable shooting platform. As that picture shows you are bracing the camera against your forehead and this helps a lot to get the sharpest picture possible, an important thing with this large a sensor.