A few things. . . . .
Seems like with the VR viewers; some people are pickier then others (referring to mirrorimage here). I guess you drive a brand new BMW 7 Series and you get a 1 year old Ford Taurus as a rental car you might think it is horrible. Personally I would be more than happy with the Taurus (of course I have never driven a new BMW though). I have a iPhone 5S and a Shinecon VR viewer and I am happy with it. For the money it is hard to beat, if I looked through someone else’s HDMI goggles I might think it was horrible, but I haven't had that experience.
I did notice with the VR viewer that I got the lenses I can adjust the pupil distance IPD, and I can also adjust the focal distance from my phone. With the VR box and the HooToo viewer you can individually adjust the lens distance from the screen. This is a plus for some as one eye is different from the other and a con for some because they have difficulty getting both lenses aligned correctly.
I contacted the app developer for "FPV Camera for DJI" and the lack of Yaw control and found out they do not allow this because it causes issues with the return to home functionality.
I contacted the app developer for "3D FPV - Stereoscopic 3D VR viewing! For DJI Phantom 3 and Inspire 1", which allows yaw control and asked about this and they told me that "we have head tracking: drone yaw and camera pitch control but you can't fly the drone in this mode. It is stationary and you look around. The next update will give you full control of the drone including head tracking while flying."
My situation is that I would like no OSD on the screen and for the image to fill the screen with no map, battery, telemetry, etc. I plan to only use this for a couple of minutes with a full battery and flying only in very close proximity with someone else actually wearing the goggles.
With the iOS apps, I don't mind paying, but I would like to be able to test to make sure the app fits my needs first; some developers are more flexible as others in regards to allowing refunds, etc.
I am intrigued by JonEQuest's post #206, never thought of doing method 3 that you mentioned but that sounds like it might work out pretty well. The current version 2 looks pretty nice, just don't feel like fiddling with that myself, but it sounds like that would work out pretty well.
Sorry to be so lengthy