Is there something specific you are dealing with that makes you want to sell it? It is definitely something you need to learn how to use. I am still trying to dial in the MFA on the long end for Eagles in my area. But this lenses learning curve is something you can/will eventually get over. Then that is where the magic happens. I just have to look at some of the images posted here by Peter and a few others users to know I have to just continue to work at refining my technique.
With that said, you do have to kind of need the lens for certain types of shots. I love shooting wildlife and moon shots, so this lens is the one that I can't give up because of those reasons. If I was not a wildlife shooter, this lens would not be nearly as needed in my kit.