Hybrid Digital Radio is different from DAB : it's a low-bitrate compressed digital stream hidden in the analog FM (or AM/MW) signal around the 100kHz region, and only found in USA.
It's useless for everyone as the signal is lost when there's noise on the analog FM signal, and the sound quality is not as good anyways because the stream is highly compressed. It's only good for two things: stations attracting listeners because they have that new "HD" thing, and iBiquity Corp. making money with the license fees on HD Radio receivers.