I personally never worked with this service but it would make sense each owner gets a box from the pair.
But knowing kitties they will make one week a better box than the other
I prefer to work with a trusted friends network when it comes to loaning a kitty or trading traits as I know them and also have some knowledge on how they will handle their business etc.
Not sure if this stud service is practised much and how it works.
I'm very curious as well about other people's experiences.