Easier to see when next to each other but in short here are the differences
GTI - is a 2 part splitter, smaller centre part that attaches to the larger part which clips and screws to the bumper. Made of black plastic.
ED30 - 1 piece, same sort of shape but is deeper than GTI and also comes in primer from factory (and hugely more expensive - more than twice the combined cost of the GTI splitter parts)
Many people do what I did and colour code the main GTI splitter part and leave the centre piece black (same goes for the Ed30 version - people 2 tone the paint)
Like so
And one of and Ed30 I found on the web