I wouldn't call that 'legitimacy', but rather 'anecdotal'. Stutter tends to vary a lot, and if there's no aggregated data to show, we can't really say much more about it. At any rate, MW isn't a speech therapist, then, but rather just someone who talks about talking. That's fair enough, of course, and it's great if it's working for you, but in terms of stuttering help, it seems a tad light.