The whole discussion of cancer in regards to mt is interesting too. mechanically they both reduce the amount you uv damage you get and decrease the amount of 'sunburn cells' you have which theoretically could make them preventative of skin cancer; but people using mt usually get more uv exposure. and activation of melanocytes also would mean rapid development of existing moles, which i way i think mt1 is much safer as its much narrower with its melanocyte receptor activation. i take mt1 and get a moderate amount of sunlight, usually my 'tanning' is a walk outside whenever the uv is highest that day, which i line up to be a few hours after i pin.
there are no clinical trials to confirm skin cancer prevention but from my understanding of how mt1 works and how melanoma works, it seems like its a tradeoff between having a lower risk of developing skin cancer (assuming you dont tan a bunch more than usual) and having more difficulty diagnosing melanoma + faster development of existing melanoma