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.
I know a little girl named Arin. Rather than using it as a alternate spelling of Erin, her parents considered it a female variant of Aaron (the name of a grandfather that had passed away). If you are wondering what the difference is, I live in an area where Erin and Aaron are pronounced differently - Erin is ERR-in and Aaron is like AIR-in. The Arin I know pronounces her name AIR-in. Although a lot of people ask "You mean Erin?" when they first hear her name, I think it really suits her.