Can someone explain this code thing to me?

So, It's time to add lifetime service to my Roamio Plus, a mini, and I want to buy another mini with lifetime.



I checked out ebay to see if anyone had any deals and instead there are a million people selling "codes" for lifetime membership or something like that



I'm not sure what it is.



I've been with tivo since the beginning. never heard of this before.



is it something illegal? or technically legal, but tivo's not happy about it? is tivo supportive? what is it???