HawkEye volume, developed by Nigel Hawks, is supposed to be a premier VSA indicator. Documentation on this is scarce (looks like the training seminars/sessions conducted by the parent company cover this in detail), if you come across any (other than what I have mentioned on that chart) do let me know.
I am not sure how much this resembles the commercial indicator out there as I don't have access to one (noticed the "clone" part? :) ). This is a direct port of a similar MT4 indicator. If you have access to the commercial indicator in another platform, do post some comparison results.