Grading the Quality of Evidence The quality of evidence was judged as moderate that treatment with SMT was associated with improved pain and function in patients with acute low back pain, which was downgraded from high due to inconsistency of results. The quality of evidence was judged as high that SMT is commonly associated with transient minor musculoskeletal harms, although they may be equally common following non-SMT manual therapy.
It's worth noting that the study itself does not consider this strong evidence.
Discussion The principal conclusion of this review was that SMT treatments for acute low back pain were associated with statistically significant benefit in pain and function at up to 6 weeks, that was, on average, clinically modest. The size of the benefit for pain (9.95 mm) is about the same as the benefit for nonsteroidal anti-inflammatory drugs in acute low back pain (8.39 mm) according to the Cochrane review on this topic. For function, the effect size of 0.39 is approximately equivalent to an improvement in the RMDQ score of between 1 and 2.5 points, using the range of SDs for the RMDQ in the included studies. However, heterogeneity was high, and could not be explained by differences in patients, clinicians, type of manipulation, study quality, or timing of the outcome. Evaluation of these differences was limited by the quality of reporting in the primary studies.
The research here suggests it is about as helpful as taking some ibuprofen in the short term. The high heterogeneity seems to mean significant differences in outcomes for subpopulations that they were unable to explain (based on context clues and some googling).
Limitations This study has limitations. First, there were limitations in the quantity and quality of the original research. More studies were classified as low quality than high quality. Nevertheless, high-quality studies tended to report larger benefits. Second, some studies did not describe the manipulation in sufficient detail to allow application in practice. Third, there was significant unexplained heterogeneity. There were too few studies to use meta-regression methods to simultaneously test for variables possibly associated with heterogeneity. The most fruitful area for further research is likely to be assessing the role of patient selection and type of SMT on explaining heterogeneity in treatment effects. Fourth, the minimum clinically important difference for these outcomes has not been well established, raising questions about the size of the clinical benefit. Fifth, the possibility of publication bias exists, although no statistical evidence for it was detected.
It is somewhat suspect that the studies they considered higher quality also happened to report better results, particularly when they say this is lukewarm evidence in their conclusions. The other parts I bolded are just important caveats.