I wouldn't spend the money on these until you've actually hauled with a loaded trailer... because it all depends on the trailer and the truck combo whether or not you need it.
My short bed crew cab Dodge 2500 (single wheel rear) needed it --- my Dually F-350 did not -- same trailer same load.
Brother in laws Ford F-250 needed it towing his old trailer -- but hasn't used it since he got my old trailer...
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