I dunno... the incessant radio chatter of ' Break left, Blue Leader, Rifle Rifle Rifle Missile away, Don't leave me Mav' would probably drive me nuts plus I don't have room for the Smart Bombs on the Ute Tray.
The cheap versions rely on a pad being stuck on the screen so risky if you put them near or in your line of sight and need replacement if you do a 'screen, the panel versions would prob be better but car dash and windscreen rake could be an issue I reckon.
I spose one day soon they will do optically true patches in windscreens and HUD will be standard.