The shield does a good job of blocking airflow through the glasses. Unfortunately, the pins that hold the shield to the frame are too fragile. This is the third shield I have purchased for these glasses. The shield has to be removed to clean the prescription insert and the lenses, so the poor little pins have a hard and short life. Half the problem is the need for frequent cleaning because the prescription lenses are too close to my eyes – my eyelashes brush them, which is an annoyance itself. Consequently I do not use these glasses as much as I would like to.
If you do not need a prescription insert and don't mind the shield getting wet when you wash the glasses, Guardyans with the shield might be five star product for you.
Guardyan Shield Interface