A friend gifted me with one of the Merit disks and it does help, but as others have said, it is a bit of a PITA to get it positioned just right, get the aperture adjusted to the right size and then to keep it there. The suction cup also blocks out a lot of the view, tends to fall off, and leaves a big smear on your glasses. The bit of tape works better with less trouble once you get it properly placed.