Well, I’d be dead if I stuck with a napro doctor, and my conditions affect 5-12% of women of reproductive age. This was a respected Canadian clinic in a major city, with a practicing doctor who had no offendes with the regulating college of physicians and surgeons. I was receiving medical care actively.
As to efficacy, I suggest you read the multi-centre studies that generated the Pearl Indexes for the major methods. A (2007?) German study for the symptithermal method included several thousand observations, and so at face value looks robust.
Aftershocks deeper dive, I was astonished at the methodological weakness in sample selection (mostly white, mid-20s to early 30s, upper middle class, college educated). There are major gaps in follow-up methodology and classification of method drop-outs, such that reclassification of drop outs as either method or user failures brings efficacy well below the least effective barrier methods (e.g. diaphragms).