You are likely to get a better response in the Goggles board, where its owners are posting stuff..
I have only just bought the DJI Goggles RE myself and fiddled with the non-flight features, such as media playback which the regular goggles didn't offer. Still plenty to read and learn on my end, as I don't live near too many open parks/fields where there's a few KM's /miles of space to fly freely
As you pointed out the Goggles dont require the HDMI board which is an extra $100+ purchase so thats the benefit of just connecting the goggles to the RC via USB just still watch in at least 720p/960p video.
RoOSTA