I know their not to everyone's taste but was hoping to get some more infomation about them as it seems Norma is wanting me to fit one to her

So I know the fiberglass ones flap around at speed but how badly and how fast before thing starts happening, also how noticeable is it?
Is there any other cars that I could get a sunvisor from that would fit the moggy?
What is the best place to get one from? Are certain places sun visors more stable than others. Would like a metal one but not up to spending hundreds.
Also if anyone has one for sale I'd be interested

Thanks
Jordan