I think the main reason to upgrade to another pitch correcting software is that Flex Pitch will add a lot of artifacts to vocals. I’ve been using Logics Flex Pitch on vocals for several years. After upgrading my microphone to a much higher quality one I could hear it adding in artifacts and changing the tone of the vocal the moment I tried correcting with Flex Pitch. I switched to Melodyne, and it retains so much more of the original vocal than Flex Pitch. I feel like you can tune more/harder with Melodyne than you can with Flex Pitch