That Reynolds plug is different; it fits into a deep-section rim like so, with a valve extender sticking out of it:
The sheer ridiculousness of these caps lies in the fact that their drag reduction, if any, will be so infinitesimally small as to be not worth even the $6.99. There are far easier ways to save significant wattage on a bike, and far more effective ways to streamline a car.
Also, I've been racing bikes for more than a decade, and I've never seen anyone using these.