I didn't get the survey invite because I just took delivery yesterday, but here's my feedback 2 days in:
It is somewhat disappointing - my wife turned it off on her profile. I find the information displayed to be too busy, too big (font size too big) and too bright (even at the lowest setting). The projected image overlaps and clashes visually with the car that I am following, even when set to the lowest setting. Optically, the image my right eye sees is a bit lower than the image my left eye sees, which causes double vision (like vertical diplopia). I suspect this has to do with the large size of the projected image against the curvature of the windshield. If I tilt my head counterclockwise slightly (like a dog tilting its head), the projected image immediately clears up. Auto brightness needs work, particularly in how it handles overpasses, the stepped brightness changes mentioned previously are distracting.
We have several years of experience and comfort with HUDs in a 2019 Mazda CX-5 and a 2019 Volvo XC90, which fade into the background pretty seamlessly and require no particular accommodations from the driver. The HUD in the Gravity, by contrast, draws attention to itself and is fatiguing to use. I will leave it enabled for now to see if I can adjust to it over time.