Oh man. No names, per J.T.'s observation ( but you can quote me by name anytime and my profile on the entries has my real state of residence, etc.)
The HUD's in the military aircraft since 1968 use the inertial system to display the flight path marker/vector and the pitch lines WRT to the Earth. Early ones had some small drift - think one mile in one hour. Short interval data was prolly a thousandth of a degree off from the real world. The A-7 used a doppler system to help keep the inertial very stable, and you could actually takeoff and align the inertial using the doppler in 15 minutes or so. Then we had GPS. With GPS we could align the inertial in a few minutes.
So negative comments about gyros and such for the HUD/main display flight path should look at the record of reliability and accuracy of such systems since the late 60's. The things work without any air data at all!!!! Think AF447, et al, and loss of air data, but a fully operational inertial system that only uses GPS for some positional data now and then, but displays your actual flight path. Would you keep pulling back stick as the troop did in AF447? I don't think so.
There are some here that have used and maybe are currently using a HUD in the commercial flying bidness. The suckers take about 5 seconds to interpret and feel comfortable. For those who have not used one, try it. The bad news is that the company will try to cram all the magenta line crapola on the display when all you really want is some basic nav guidance and your flight path vector to achieve the desired profile.
Sorry if I continue to rant, but I went thru all the advances in avionics and displays since 1971. I never had to see the FMS stuff and the "magenta line" due to my bidness. I never flew a jet that had auto-throttle, or an otto that flew the climb to altitude with all the heading changes and such. I used otto for heading hold and altitude hold and such, especially on long missions while I snacked on a candy bar or ate a box lunch. Think 13 hours in the chair you are in right now reading this.
We have many tech capabilities to help the crews, but we still have to possess basic flying skills and use all the available tools/displays and such of our planes to get where are trying to go. I have a problem with crew coordination, as most of my time was single-seat. So I defer to those here with all the experience.
So that's my input for today.