Further to my experimentation.
Got a cheap tablet (xGody) that had HDMI output. Glyph worked bu open ROV app no video. Anyhow, tablet died after 24 hrs and has been returned for refund. Would not recommend.
Have had all kinds of difficulty finding a tablet that will do hdmi output. Ordered one of better quality from a local shop but is on backorder and wont arrive for another 3 weeks.
Has micro HDMI, a mediatek rather than rockchip processor, Android 7.1.
Have tried HDMI adaptors with no success Android support for MHL or slimport is a very hit and miss thing.
Mira or Chrome cast possible i guess, but the adaptors need 5V/1A power which is not easily do-able in the field.
Best solution would be an opencockpit app that is easy compatible with a Google Cardboard type headset.
Could run the Trident off a phone wireless in that with a controller bluetoothed onto the phone.
The config of the Avegant Glyph is good though. Safer in the field or on a boat as can look around it rather than something sealed to your face.