Of course you'll also need a long lens with a rotating tripod mount collar. The Sidekick is designed for lenses in the 300mm 500mm range. As the instruction manual so rightly points out, you now have something like 6 lock knobs to pay attention to, between the ball head, the Sidekick and the lens collar. Murphy's Law will always apply. The first day I used this set up, when I finished balancing the lens by sliding the plate I forgot to lock the knob.
New gear requires new habits and a bit of extra attention to locking all knobs is required.
The Wimberley Sidekick is the product of a small father and son company. Its design is simple, it does exactly was it sets out to, and does it extremely well. The Wimberley Sidekick as well as other products of interest to wildlife photographers are available though Naturephotographers.net King Cobra Kirk Enterprises now has a comparable product to the larger Wimberley Head called the King Cobra.