The device must, 'emulate(copy)', a keyboard, mouse, or graphics tablet. (Input device)
If there's something your mouse or keyboard can do with the software your using, zoom in/out for example,
this device could do the same by picking up your hand movements.
The writing on screen is more complex, the software on the computer would have to be geared up to accept this type of input.
It looks amazing, but to Joe Bloggs, not worth £50. He won't be able to use it on a daily basis without specialist software.
IMHO of course
Hope you get my drift.