It claims the microspheres are air filled. The following URL claims that their spheres have a vacuum.
http://www.hytechsales.com/insulating_paint_additives.html
The Hy-Tech spheres added to epoxy on a woody roof could be an interesting experiment.
From personal experience a small RV suffers from radiant solar gain, so it seems a reflective coating would be a good thing. I can feel the sun's warmth through our Chalet's low mass insulated panels (1/24" fiberglass, 1" foam, 1/8" wood) instantly upon sunrise. R-values don't tell the whole story. Filon has much better R-value than aluminum, but aluminum reflects radiant heat much better.
That said, lots of claims from both companies without a lot of test data to back it them up.