I just bought a random bed extender on Amazon, after putting it together and test fitting it to the bed, it doesn't go all the way to the back of the tailgate, I gain maybe 19-20" extended out.
There's someone selling an Amp HD sport with the sharper center but from all the photos, it seems to extend further. I prefer the squared corner to give more real estate so I'm kind of stuck deciding if I should pick up the used Amp HD Sport to just bolt the generic brand onto the truck.