If you have already registered your Horizon product to another format then you have to buy the "side license" which is about 10 % of the price of the full product. If you are a new buyer then you can select Kontakt as your format and there is no extra cost. If you then choose to change the format you have to buy the side license. So basicly you have to pay the side license when you change the format of a registered Horizon product.
Well in a sense that is true. You have to be registered to get the Kontakt programs but you have to register the product straight to the Kontakt format to get the programs free. This seems rather silly to me as I can't use the GigaStudio versions of the samples even if they are already on the installation DVDs. Not that I want to but still it seems strange.