I don't know it helps you, but Frontline complexity is lower then Down in Flames. We affraid to go to vacation without DiF rulebook, but I can play freely Frontline without rulebook, after a few study-play.
I would want to take the frontline rules with me when ever i played so i could choose all those missions. Although I feel that complexity wise, DIF is easier but thats because i play it alot. I'm sure frontline will become the same. I think there is slightly more depth in frontline.