In another thread,
@Handle123 has mentioned the work of John Hill. A few of Hill's thoughts that seem pertinent here come to mind: First, the point that "a person's trading psychology can make or break a trading plan." All the rules and the best laid trading plan won't make you money if you lack the discipline and ability to adhere to those rules and follow that plan.
Second, and more directly relevant to this discussion, is the distinction between what Hill calls a "precisely defined algorithm" and a "loosely defined algorithm." A precisely defined algorithm "would and should" result in similar overall results amongst those individual traders trading that method. A loosely defined algorithm has no exact parameters, and as a result, "if two traders were to follow this approach, their overall result would probably be quite different." These quotes can be found in chapter 8 of Hill's
Ultimate Trading Guide, along with examples of a precisely defined and a loosely defined algorithm.
While I know nothing of this "SLA" method other than what I have tried quickly to gather in order to understand the backstory to this thread, my impression is that its advocate/author was presenting a "loosely defined algorithm." The fact that he/she seems to have placed great stress on the need for each individual to proceed to test the method and develop an individual trading plan indicates that he/she was well aware of the loosely defined nature of the "SLA algorithm." While he/she was aware of this fact, it would seem many are/were not.
Those who do not accept or understand the distinction between precisely and loosely defined trading algorithms, and who expect all algorithms to perform "out of the box" in a precise manner, would likely fail any attempt to apply a loosely defined algorithm without first developing rules, as
@NoDoji suggests, for trade management, e.g. not only when/how to enter, but where to place one's stop, when and where to move one's stop to reduce open risk or capture open profit, when and where and how to take profits. So as to whether the SLA algorithm has "worked" or not is really not the proper question, as its working or not working is going to depend entirely on the abilities of the individual attempting to "make it work."