We're asking users to (hopefully) register which datasets they'd want to use before they end up in the datasets download page at /datasets/download. But once they get there (or if they get sent there directly by someone sharing the link / skip the registration) they have all the datasets available, including the ones they have not registered an interest in.

IMO it would make sense to track the specific datasets the registered user has listed as being interested in, and show something about registering their interest by any ones they have not registered for yet. If they are not logged in or haven't registered for any datasets we should show the same for all datasets.

For example, we could have a "register my interest" link on each box for datasets the user has not yet registered for - leading to a signup page if not signed up, or to the edit profile sets page if they have.