Just got back the first test exposure using this technique. Makes for great balance between foreground and sky, but one must be very careful about aligning the mask. I shot the first try using a fence as my dividing line, and if you don't stop the lens all the way down to the taking apeture, you will be fooled on it's placement. You will wind up with either a bright line or a dark one that will destroy your work. The same as with a Grad ND, but here the error is more evident as you are totally masking the sky. It does look as if it is more difficult to use than Grads, but it can and should produce more precise results.