My own concern with this type of method relates to the subject of "scaling". With modern charting packages, as you move up or down in price, there is an automatic scaling that takes place. This may change the position of your datum points (the points from which you originate your rays). On a paper chart of the type Gann would have originally used, this was not an issue. I have to confess my bias that work of this type, Gann, Ellliot Wave, Fibonacci, Astrology, tossing chicken bones, coin flipping, and so forth, may not be as productive as simply taking the time to learn to interpret supply and demand. If you are a devotee of Gann methods, I hope you will not be offended. That is not my intention. To be fair, the obvious question to ask is if reading price and volume (supply and demand) is more effective, why do so many traders lose money with it. From my point of view it is because there is a lack of good education on the subject, and because most of the traders who use it simply aren't very skilled.
Best of luck with your trading. Steve46