Short answer-- DON'T USE THEM! They are NOT REFUNDABLE. One of the two of them implies it MAY be refundable depending on the fare rules. I spent 20 min buying some, going over fare rules to ensure I was getting refundable ones.
Two months later, they wouldn't refund them, every person I talked to told me flat out NEITHER was refundable, and I had my non-rev privileges threatened when I asked agent to actually LOOK at the ticket fare rules I had printed out with the tickets showing it WAS refundable.

I've never been as mad at the company as I was then... don't try to save that bogus 10%, it's a scam and you can't trust them-- you don't even get to go through a normal agent, they are all "special reservations" agents for travelnet who basically are in place to stiff arm and threaten you.

Sounds harsh I know, but after going to soooo much effort to ensure I bought refundable tickets, getting $4000 stolen from me administratively by the company taught me my lesson. Now I no longer try to purchase tickets on Delta to help the cause.