Mersincik is a bay at the north west end of the Datca pensinsula. The bay offers fairly good shelter if you’re lucky enough to get a spot at the west end, less so in the middle of the bay where there can be some swell.
So in calm weather it’s fine as a night stop but otherwise I’d head elsewhere.
It’s a pretty spot, but you’ll need to dine on board as there are no restaurants ashore.