AnnJ,
Registering does not require purchasing. You just register with the licence key that was displayed + mailed to you after you asked for the free software.
On my first attempt, it seemed that the registration did not “stick”, and that I had to apply it again at next launch. However, the problem corrected itself. (I had this problem once with another SoS offer : that particular software still asks for the key everytime it’s launched. Irritating.)