Upload & Sell: On
If a contraption functions like a Gimbal mount, is it a Gimbal? As a blind test, let's put a shroud over each of the heads mentioned in this thread I dare say that one would be hard pressed to tell which is a Mongoose, Sidekick, Wimberly II, etc. as far as shooting functionality goes.
With a little thought, it would also seem that the torques and stresses in each of the heads would be essentially the same regardless of the design. Except in regards to things like length of the arms, of course.
A choice of either of these design would depend on whether one prefers an assuring stable horizontal platform on which to mount his or her expensive Super Tele, or an arguably less safe sidekick- like design with its accompanying weight loss of a pound or so.