In theory you absolutely need both, and the library fixes the most pressing issue: that your site might be broken today, and more importantly will remain broken

In theory you absolutely need both, and the library fixes the most pressing issue: that your site might be broken today, and more importantly will remain broken forever, unless the user chooses to upgrade, since Safari does not do automatic over-the-air updates (ala Chrome on desktop) but instead bundles it’s updates with OS versions on mobile, and updates that may or may not be set to automatic on macOS. As such, you should in theory now always have a bug-detect in your code (simple to write, make two identical 2-item arrays, reverse one, check for a difference), and apply the fix if needed.