I do not know the brand, but just out of common sense the race version will be definitely MUCH louder than the homogolated KAT version. You may even get fined by Police if they catch you that you put the race version on. But contact the manufacturer and see what dB rating the race and KAT version have... let us know what you found out.
Did you check what they bring individually on HP on a graph compared to the OEM KYMCO exhaust?