I find the design and results somewhat underwhelming (weak significance in a N=800 sample with >50% dropout). The authors also mention that they lack power, but the only correct answer then is not to do the study, include more people, more data points, or reduce measurement variance.

That said, I think it's a refreshing perspective, and it seems like a good idea to look at effect heterogeneity in psychedelics use. Thinks like bayesian trees (BART) can help identify subgroups that react differently to stimuli along specific characteristics.