You have more faith in people's manners than I
No no i understand what you mean, folks just buy them these days and think they can fly them anywhere how ever they please.
Like the bloke in the vid there are lots of responsible fliers out there, if it's a responsible flier chances are even if it's directly overhead, unless there is no wind at all chances are you wouldn't notice it.
The optimist in me recons that if someone goes to all the hassle of lugging one up a hill/mountain then they'll at least have a idea what they're doing.
Besides even with modern electronics IF they fly too low a decent gust of unexpected wind and they'll lose it.
I did faff about setting up a glider for hiking vids years back, my logic was that i wouldn't have to lug heavy battery packs up and down the hills (they still need smaller batteries for the control, but these tend to last a fair while).
Didn't count on how tough it was to fly a glider though
Be a good low impact (on environmental noise) solution for those that can fly them