Works good for awhile , Still Experimenting
I use this product on my SeaSpecs Ocean Sunglasses to paddle and surf on my belly/kneeboard. How long it works well for is based on wind speed and direction and surf intensity & height. 10-20mph wind, no surf for about 30-45minutes it works pretty good.  2 feet surf 10-20-mph  it last 30 minutes to an hour depending on how you protect your Sunglasses in the surf. Please Note: I am still experimenting and when I mean works well is when water does not bead and sit on lens. I have only tried 3 different brands but Z Clear works the best.
Rating: 4 stars