Sorry for the late reply. I use a Wimberley Sidekick with a Kirk BH-1 ball head as works better for me as I can quickly go from using a long lens to doing landscape/macro without having to change heads or having the extra cost of a full Wimberley and a ball head.
I will be keeping my sidekick as I intend to use it later down the line when I get a Nikon 200-400mm. As far as I know they do not recommend the sidekick for the 600mm and say the full wimberley is required, there is a lot of information on this at Art Morris’s website http://www.birdsasart.com.