"Forehand fixing machine"

In this video starting at 1:46 Ariel Hsing puts on what she calls a "forehand fixing machine"

What does it do exactly?

My guess is that through resistance it tries to limit the mobility of the elbow which promotes proper stroke of the forehand counterdrive which can be a whole topic itself.

I made one of those for myself several years ago.  It helped me a lot, my forehand is just better in every way when I keep my elbow closer in, and this is true even though I like to play away from the table some.  And that's what this little device does, it keeps your elbow close in.  I am thinking about digging it out of the closet after seeing this.  It won't help everyone, that's for sure.  In fact the more modern way of hitting a forehand that you see in a lot of Chinese players would actually be messed up by one of these devices.  But my stroke is what it is, and I learned to play a long time ago.  It also forces you to move more and it has this side effect of improving my ready position.  It can be useful for all kinds of players who hit the ball a certain way, Ariel is obviously not a beginner or intermediate player.

Edit added.  One reason I stopped using it is because a lot of my clubmates thought it was a really stupid idea.  So I am actually happy to see that not everybody thinks so.