I'm an engineer, but not a sound engineer. Comparing their test data to other IIC STC reports, their results are comparable to similar flooring systems that did not use their product. I suspect that most of the reduction in sound transmission comes from the other components in the test floor. They did not perform a comparison test between the floor with and without their product, so I can't say definitively.
From the companies literature,
Results: What is truly important considering Solid Sound Plus ?
Most people use SS+ to reduce the hollow, "reflected" sound commonly experienced with lower quality foams used beneath "floated" floors.
The company does not claim this is some miracle product to stop or even reduce sound transmission, just modify its profile. I think you and your upstairs neighbor were expecting more. This stuff is only 2mm (1/16in) thick, so I would not expect much reduction in sound transmission.
I also found it interesting that they claim an R value of 3, but as is typical in the insulation industry they did not specify the test conditions. So if I fill my walls with this stuff can I get R-135, probably not.