Hi, the biggest difference I find with the ZED fares vs the ID 90 fare is the flexability. For example, if I want to go from BWI to NAS I would purchase an ID90 fare on Delta. If all their flights were full on the day of travel, I would have to purchase another ticket on AA or US. Now I have 2 tickets to NAS (out double the money) until I turn my unused Delta ticket into my airlines for re-imbursement.

Now if I have a ZED ticket: if I am unable to get on the Delta flight, I can take that same ticket to any other airline that offer ZED fares just as long as the routing is the same ie if I purchased a non-stop, they generally want you to fly non-stop. I always have my airline book a connecting such as BWI-ATL-NAS so that I would have no trouble presenting to AA for a routing of BWI-MIA-NAS or US BWI-CLT-NAS. I love the ZED fares in that it is much easier.

As for your registered partner, I think that you will have to check with your airline.