Review (4/5): Here's the deal...
These do what they are advertised to do, but results will differ based on a few variables. Remember, the goal is to breathe *through* the mask, not around it. So when there is a better seal, it might be less comfortable to breath.
First, These are memory foam and come vacuum packaged. After you open the bag they take a couple of days to expand to full size. If you use them before they have expanded they will be misshapen and not fit well.
They work best on disposable masks with an adjustable nose wire. The adjustable wire is essential. When you attach the pad centered and directly beneath the nose wire, wear the mask as normal, then squish it onto your face firmly starting in the center of the bridge of your nose and working out. Your ear straps also need to be tighter to maximize the seal all the way around the mask.
Will is stop your glasses fogging completely? no. Is it much much better? yes.
Here is a ranking of performance characteristics.
1. Stability - does a great job of keeping the mask on your nose (assuming a nose wire on the mask).
2. Comfort - significantly reduces abrasion on the bridge of your nose.
3. Seal - this depends on your face, the thickness of the mask, and the strength of the nose wire. I get a pretty good seal and am no longer exhaling directly into my own eyeballs.
4. Reduce glasses fogging - This is directly related to the seal above. It's way better than nothing, but not perfect. I still get a little fog if I breathe hard, but no longer while talking.
Overall, I am very happy with them. They are a significant upgrade, especially to 3-ply surgical masks.