Earlier quoted context omitted.
Why not? The videos show the devices being operated with one handle fixed against a wall/door. In that situation, nothing flying off the disc will go towards the operator. You could also enclosing it in a box or operate it inside a hole in the ground.
"nothing flying off the disk will go towards the operator". What about other people? As you say, you can enclose it in a box, but that means making a glovebox, which increases cost significantly.
The device only requires a single person to be present.
> that means making a glovebox, which increases cost significantly.
You don't need a glovebox, you just need a way to pull on one of the strings from outside the box.