only difference really will be the build quality they all will work but some will not last if you just chuck them in a bag of gear to take with you but all work relitivly the same. its a topic that has been brought up lots here
The foam was specially selected to give maximum pop protection without changing the character of the sound (you get two foams in the kit) - also the frame is pretty invisible to sound waves to you don't get any HF reflections off the frame.