I would suggest that you only get one at a time. It will definetely hurt too much for you to fall asleep on the ear with the cartilege pierced for a least a couple of nights, and even if you fall asleep on your back, you'll probably roll over during the night, onto the ear you got pierced. If the pain doesnt wake you up, then it'll hurt alot more in the morning. Also you should see if you like it on one side, before you get the second done.
I had mine done with a gun and it didnt shatter the cartalage. I'd say that that is a pretty rare thing.
I wouldnt get it done at claire's. The employees there are not professionals and only have the basic training for piercing ears. Getting cartilege pierced is a bit trickier than piercing lobes and I wouldnt trust the people there to get it right. I'd suggest going to someplace that specializes in esthetics. Try a hair salon or a place that does manicures. Many of thsoe places also offer piercings, and actually have more training and more sanitary conditions than claires.