> You can't use one of these on a train, tram, bus, plane, or in any situation where there are people next to you.

Oh you can. You just use the display that gets slided at the front position.

> And even when there is enough room, you pretty much instantly give up any semblance of privacy.

I have a 3M display view protector foil. Works quite well, except if the spectator is directly behind you.