Disagree that it is "high gain" or that it is "digital HD"?
High gain is real, although it has the downside of being highly directional so you must aim it. The one you linked to doesn't list its measured dB gain so I would be skeptical of it w/o more research.
Digital/HD is just marketing hype that has nothing to do with reality. Antennas are tuned to specific frequency bands (really specific frequencies). How the signal is modulated - AM analog, FM analog, FM digital, makes no difference.
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