The problem with Gann is, you have this scattershot of lines and squares and 'rays' all over the goddamned place - so eventually price will reverse from one of these lines and form a top or a bottom - but by pure chance.
To the Gann practitioner, however, this meant that the "1x4 Line Is Strong Support" or some such nonsense. To the rational price technician, it just meant that overlaying a bazillion lines means you get some kind of coincidental intersection.
I find his time-related work more interesting, but its of the simple variety using the square of number representing time interals and such, and the same thing applies - you throw out a million different combos, and one will "stick" eventually.
The Gann trader I know would wax poetic about all the seeming "confirmations" that price had on a chart overlaid with a thick haze of lines, and all I could think every time was "no shit, you have very little on that chart that ISN'T A FUCKING LINE."
I wish I could give you a happy ending to that story, but the Gann trader I knew doesn't really trade anymore. I guess you could say they never knew how to trade, and the market made sure to deprive them of any capital to continue their self-fed delusion.
Reading the article and researching some more around I kind of got to your very own conclusions. I personally don't know anybody who has ever used this method but I kind of understand why.