I have found the optical quality on those filters to be fine.
I have been using filters from Phantomfilters.com for a while with a good experience. I store them in the little plastic sleeves they came in.
Knowing they are fragile, I baby them. So far, they have been great.
I like that they are light and fit into the stock lens cover. The gimble on the P3 seems lightweight and doesn't need any additional weight added to the front of the camera.
Eyeglass lenses aren't glass, they're made of plastic