The difference is that a conventional wing will produce lift at 0 angle of attack but with a symetrical section you need to fly a + angle to produce lift. The advantage is of course that it will do it as well whichever way up the aircraft is flying whearas with an asymetrical wing it will work very well erect, but NOT inverted.
If you think about a vertical climb the assymetric wing will produce lift and hence needs to be flown forward of the vertical to go straight up but the Extra will fly straight up when pointing that way.