Addendum: I tried it again with heavy cream this time. A definite improvement. One thing that I deviated from the recipe this time, I mixed everything together from the start, adding the cream last to minimize "curdling" by the lime juice. It created a better feel to the drink. I also just dusted the top with Graham cracker crumbs. The whole rim made the Graham cracker flavor/smell too dominant. So my recommendation: use the cream instead of the half & half and, if you can, use key lime juice.
I thought to myself, no way this will taste like a key lime pie. I was wrong. Not 100% key lime pie flavor, but pretty darn close. I substituted Nellie and Joe's Key West Lime Juice for the regular lime juice for a more "authentic" flavor. I used 1/2 & 1/2 but will try cream next time. The 1/2 & 1/2 was a bit thin and I would prefer a fuller texture on this drink. Second one I added 1/2 oz pasteurized egg white and just dusted top with Graham crackers, much better mouth feel.