I would imagine it means that even though it's raining your hair will remain straight, no reversion and no frizz! Can't be bad!
Ah I see in that case I'm looking forward to it raining. I'm interested to see what it will be like tomorrow after sleeping on it.
Kookie I would say it would be fine. My hair is quite fine but with an annoying wave and frizz if left to dry naturally and it has given perfect results. I would guess it gives better results than it would on thicker hair or really curly hair.