My shaky hunter it didn't mater about the cock feather up or down. I used small diameter Quik Spin vanes. The larger diameter vanes might be an issue with cock feather down. The things I found with my Shaky hunter was bounce back. it dropped far enough but would bounce back up and make a thump doing so. I put some hot glue and mole skin under the drop arm and it seemed to help make it more quiet and I never tried a large profile vane cock feather down again to see if I fixed the bounceback problem.
Over all the shaky hunter is a good rest, most drop aways make some noise. Still looking for one that is silent, Until then, the price is right and if you shoot cock feather up you should have no troubles.