Iknow of it, Herbalgram did an excellent review article on it, 10 (?) years ago. I have not used it as good quality material has been very difficult to source. There are some standardized extracts in the marketplace and I have had some reports of signifiant antidepressant and anxiolytic activity, with little or no adverse effects. Here are a few recent articles on Kanna, both are free full text on PubMed
A Chewable Cure "Kanna": Biological and Pharmaceutical Properties of Sceletium tortuosum.
Manganyi MC, Bezuidenhout CC, Regnier T, Ateba CN.
Molecules. 2021 Apr 28;26(9):2557. doi: 10.3390/molecules26092557.
Sceletium for Managing Anxiety, Depression and Cognitive Impairment: A Traditional Herbal Medicine in Modern-Day Regulatory Systems.
Brendler T, Brinckmann JA, Feiter U, Gericke N, Lang L, Pozharitskaya ON, Shikov AN, Smith M, Wyk BV.
Curr Neuropharmacol. 2021;19(9):1384-1400. doi: 10.2174/1570159X19666210215124737.