What's the deal with fan types?

[lngbed71]

As of late I've browsed across posts about how bad flex fans are, and how they break and mess up everything under the hood. I don't get it, I've run them as long as I can remember and have never had anything go wrong with them. I have read where the "flex" part of them will fatigue and break over repeated flexing and such, but again I haven't heard of or experienced anything like that. Is there something I'm missing or is it because I getting "aged"? Are there any articles and what-not about the safety of these flex fans someone can refer me to? Any help appreciated, thanks
JK