Haven't used a mechanical rig such as the one you have posted a link to, but I do use bean bags to support the length of big whites (300 f/2.8, and more relevantly perhaps, 500 f/4), and find they can help by giving greater stability, especially if in a strong breeze, for example, by damping/supporting the end of the lens.
It may be a matter though of horses for courses for a given subject matter, because the drawback I would expect of the item you are looking at is manoeuvrability if you are looking to track a subject in more than one plane.
Gimbals provide great movement, whereas the extra stability of the support you are looking at might be best for a static subject where tracking movement isn't required, such as a nest site for example.