Ingress Audio Engineering

Geoff's excellent post has refreshed my memory. The concept of the roller bearing is a compromise between maximum isolation capabilities, and practical considerations. A set of three ball bearings between two flat, very hard, very smooth surfaces would provide the maximum isolation possible. Those surfaces could be the bottom of the component to be isolated (or something harder and smoother than it, onto which the component is placed---no rubber feet; put something with no compliance between the component bottom and the surface. Barry Diament recommends ceramic tiles, available for pennies at home stores) and another flat, hard, smooth surface (again, that could be a ceramic tile). But that would make possible the component sliding right off the rack or shelf it is sitting on.

For practical considerations, a pair of bowl-shaped structures are used in place of the flat ones; the bowl of course makes the component sliding off the ball bearings impossible. Now, the shallower the incline in the bowl, the better the isolation. When the ball bearings are presented with vibrations, they move microscopically, being forced to climb the incline of the bowl. The bowls' incline thwarting the movement of the ball bearings creates damping, a thing very different from isolation. So, the shallower the bowl, the gentler the incline, and the greater the isolation. That's why the larger bowl carved into the Ingress cups makes them superior in design to the Symposium.

The original Symposium Roller Block used cups on only the bottom, with the ball bearing in each of the three cups contacting the flat surface of the component to be isolated (Symposium makes little stainless steel plates for use under components, for the ball bearing to slide across). The Roller Block Jr. (and the original Ingress) used a cup on both the bottom and top, the ball bearing keeping them apart from one another. Barry's Hip Joint design called for a bowl on only the bottom, for maximum isolation. A cup on the top does, however, provide insurance against the component sliding of the bottom cup. If you want to play it safe, go with the double-bowl design.

The degree of hardness and smoothness of the bowl also effects its' isolation capabilities, the harder and smoother the better. That's why the 7075 aluminum of the Ingress V.2 and V.3 is superior to those made of the softer 6061. The V.2 and 3 all also polished with finer grit than other bearings.

As for cost, the bearings are sold in sets of three. Those sets are far cheaper than even one footer offered by other companies making isolation products. I agree with @rsf507, they ARE dirt cheap!