Doesn't look at be any difference other than the tailpipe diameter, least according to the product summary.
The reviews I've read about them are favorable. You can also make your own set of free-flow pipes like myself and several other C4 owners have done. Cheap way to get the exact look and wonderful sound, at a fraction of the cost.
There is some resonance but I honestly like it. If resonance bothers you then you might not want these. If your switching from your stock mufflers then youll notice a much more throtty sound and a smooth rumble at idle. Definitely a big improvement from stock, plus it looks good!