I have a jack splitter, and a big jack cable to GoPro's USB port.
Works pretty well overall - but I had to get an open shell case for the GoPro, and have a cable dangling to the camera. It also not possible to charge at the same time as record sound which is a little annoying.
Sound is pretty good quality - but remember that if you're plugging it in, in the back with nobody there - chances are that the sound may be too loud or too soft, so adjust it on your com panel, and test it before flight. I've had videos ruined by that!
Hope this helps!
Alex