I pronounce it AIR-ee-in. It's very nice sounding and I can definately see the name potential, but it's too similar (and is identical sounding) to arian. Like, what the Nazis considered the perfect race. I wouldn't be able to look at the name without thinking of the Holocaust. I prefer the sound of Arien to the name Aerin, but would never use it. Also, why not just
Erin? Or perhaps, if you're looking for something a bit more original, Aeris?