Arin is my middle (I am female). The reason my parents spelled it like this is because they wanted it to be unique. My dad's middle name is Aaron, so they combined it with the female spelling, Erin. My best friend's name is Erin too, so it's funny.
I prefer the spelling Erin, but I think this spelling can be cute. My brother and his wife considered using it as the name for their daughter because his name was Aric, so it would be the same sort of variation.