It is time I took some images with and without mounting the X4 Circular Polarizer on my Summicron-M 50 mm F/2.0. Because of limited time I could spare, I only made two sets of images to illustrate how the X4 CPL works to remove reflections and glares from shiny surfaces.
In the first set, I took an image of the gloves.
Notice the reflections under the gloves disappear in the second image when X4 CPL is mounted.
In the second set, I took an image of a photo frame on my desk.
Notice the picture in the second image shows clearly after X4 removed the reflections on the glass. This demonstrates the capacity of the X4 Circular Polarizer.
One thing not working really well with the Leica M is that I need to use the Leica EVF 2 or use the Live View on the rear screen in order to see the distinctive effect. If you look through the rangefinder (optical viewfinder) of the Leica M, you are probably hard to tell the X4 is in action. Of course there is absolutely no issue on a DSLR.
After all, the X4 Circular Polarizer is made in Germany. You should have no doubt on its quality.