One other thing of note: the offers only show Ding! fares from the city of interest.
For example, if you have put MDW and not CLE, MDW-CLE fares will be shown, but not CLE-MDW. For that, you'd have to look on the flights page (as part of a roundtrip, for example). It also could foul up same-day Ding! specials, because these would have to be booked roundtrip (which eliminates the opportunity to check in for both flights online) unless you want to make changes to your city list.