I agree with what you seem to imply here: if Plask is free, that means that Plask is not the product but its users are the product. They are probably building a kind of database from all information (i.e. videos) shared by the users with their application.
This being said, the results you shared looks not too bad at all ^^
PS: any chance to see you dancing? :D
RE: PLASK.AI Review | Motion capture accessible for everyone