Notice what Bantai says: “By the way, the Registration backup service that costs 5.25¤ is not mandatory and can be removed from the order. It is a bit intruiging that SWREG has made that an opt-out service.”
You receive a login to the Renoise backstage area where you can download your full version. There is no serial/registration key needed. You download a version of Renoise which has your personal details embedded into it.