Must be something wrong with the search function then!
But to save you some time, I'll answer this really quickly.

Economy Flex (as it is now known) is available on all SAS intra-European routes (not Scandinavian and domestic routes) as well as intercontinental flights (incl CPH-SEA).

On European routes (BCN-CPH for instance) - Flex passengers sit right behind business in front of regular economy and receives free food/drink service.
On intercontinental routes - Flex passengers sit in a separate cabin with better seats and legroom. More detailed information on prefered seats etc available with a search (sorry) or through SeatGuru. Basically Economy service with better seating.

On intercontinental routes buckets Y and S give you Extra/Flex seating.