Is the "low profile" HUD any different than typical ones? Also why do they mix up the HMD? Is the HMD going to replace HUD by using some kind of parallax-free m

Is the "low profile" HUD any different than typical ones? Also why do they mix up the HMD? Is the HMD going to replace HUD by using some kind of parallax-free motion-compensating technology? I'm confused by the article.