The demise of NW has reduced the usefulness of Expertflyer for those trying to burn DL (or other ST) miles. I recently subscribed to KVS, which shows DL O class (award) availability. Expertflyer has added many airlines over the years, but KVS has an edge in the number of airlines covered. Expertflyer has an edge in that it allows searches over several days (+/-3). My new verdict (as someone who redeems several million miles each year) is: You may well need both.