I am not sure if X4 Circular Polarizer started at the beginning as a Kickstarter project, nor if it was introduced on Digital Photography Review or earlier. But I am certain that at the beginning they did not have a plan to produce a filter size as small as 39mm for the Leica M series lenses. I read their website and was interested in a polariser filter for taking photography. All the filter thread of my current M lenses are 39mm. I do not need a converter.
I remember I wrote a feedback to suggest there may be a demand of the size 39mm. A gentleman of Breakthrough Photography replied to me that they would consider. Later on when they launched their project on Kickstarter, surprisingly the size of 39mm was included. Although it costs a bit higher than I expect, I was willing to support it because the company kept its promise.
So what is a polariser filter? The definition on Wiki says, “A polarizing filter or polarising filter is often placed in front of the camera lens in photography in order to darken skies, manage reflections, or suppress glare from the surface of lakes or the sea.” It is essential when you take images of landscape and nature.
Several days ago finally I received a small package with the X4 Circular Polarizer in it. It was in a nice packing.
I have not had any time to open the box to try. But if you are keen to know X4 Circular Polarizer competes with the other brands, visit this link. I will do some testings very soon.