If you have limited space, it's a good variety to have.
I don't know about rare though, there are a lot of people in Southern California with an Oroblanco in their yard.
Oroblanco is known to be a bit hardier than other grapefruits, though I don't know if it's as hardy as its parent, Duncan (one of its parents).
Still, I don't know if it's going to be able to survive outside for you where you are. (presuming you'll be using some protection)
I'd guess it probably isn't going to be able to survive in the open with anything less than 9b.