They are probably experimenting with sandwiches of high refractive index material. There are no statements regarding transmissivity, which leads me to believe

They are probably experimenting with sandwiches of high refractive index material. There are no statements regarding transmissivity, which leads me to believe that its actually lower than a typical lens wide open i.e. the incident irradiance (light on the sensor) is equivalent to a regular lens set to a narrow aperture. There is no free lunch in optics or physics usually.