Is there actually any difference between the two? Other than a code to get the special friend chat? My brother and myself have traded the code, yet there seems to be no difference or benefit to having the extra steps of kinship. I would have assumed perhaps a slightly easier or less restrictive chat filter... no, perhaps a special chat field for just us... no, an actual reason to register to use it... none, anything to it that i may be missing?
I think its just so you don't have to be online for your friend to add you. You just give them the one time use code in real life and they type it in to add you when they get the chance. And by one time use its not for everyone it has to generate a new code for each person after the previous code has been used. If not the previous code is void now.