As a very general rule, DL imposes high fees on award tickets originating outside of the USA. DL also has long blackout periods on KE, much longer than the carrier imposes on its own FF because DL blacks out all KE flights on any date where a particular route/direction is blacked out by KE.

IMO the DL program is best for those who can do high mileage, 75K for PM or 125K for DM, while the best benefit is free upgrades into FC on DL "domestic" (North American) flights. There is also concern on the DL forum about rumored possible changes to make the program more revenue based, so there could soon be major changes not to your advantage.