I have used them for over 30 years.
Never had a problem.
I have one on my Ray Barton 472 Hemi. (70 Challenger)
I have one on my 440 68 Dart.
I have one on 318 Poly 66 Coronet.
Over the years I've had them on over 30 cars.
Just for the record, Ray Barton himself told me when he saw my Challenger that he does NOT like aluminum flex fans.
Go figure.