I have one. It works well if it's not too windy. On one of our Southern AT summer section hikes, we all took nothing but Seattle Sombreros for our rain gear. This worked okay during a rainy July hike.

If it's windy, the SS is not as useful. In recent years I have worn my hemp Tilly hat, which works as both a sun hat and a rain hat. It leaks a little rain when it's coming down really hard, but does a little better in wind.
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--Ken B