When do I use an S.F.I. Flex plate

Thank you all....I have never seen a SFI rated flexplate and I didn’t know if it mattered. Plymouth 65 post brought it home for me. The design of the OE flexplate allows for movement and there is no way to know if the metal has started to fatigue.

Just ordered one for me as an early Christmas present. Thanks for providing your opinion it really help! Merry Christmas everyone.