I have both the Griffin and the Belkin adapters. I had heard that when the Belkin came out it was too long, not sure if they changed it, but it is only about a little over an inch sticking out of the phone. that said, I wouldn't use it in my pocket or anything. I bought it for my desk at work to run into my desktop speakers. I have the Griffin for my car or headphones usage. I like it because it is very flexible. longer but flexible. They are both available at an apple store so no reason to go online.
and for $15 instead of $10 you can get the griffin with a splitter attachment that has independant volume sliders. nice for a movie on a plane.