It does not make any sense as it is much easier to just use your fingers as in many of the other Theremin applications... But was bobbing and weaving my face in front of my telephone yesterday evening and that kept me entertained for about five minutes!
Ohh yes it is for free- so for this entertainment you do not have to pay anything.
Also do not like to make fun of anyone but if you write the following grandiose description you kind of have to blame yourself.
From the Playstore description:
"This is to the stylophone and theremin what the electric guitar was to the lute.
In the future all music will be made this way.
Do you want to be part of the future?"