If you click on flying bombs read the description,it will give you an idea what it's good for.
You can use it to bomb province's morale and economy(can't recall the exact damage to a province with full morale)If you can master their use you can become a huge pain in the butt to your enemies.
Flying bombs are cheap and fast to produce.If you have multiple secret labs you can build a few daily,adding it to your flying bomb stacks.They are useless against AA (rockets are not)
For Allies a 10 stack flying bomb has a 115 attack... Comintern 10 stack has 90 attack,so the bigger the stack the bigger the damage or multiple stacks, multiple damages.
You can utilize flying bombs to attack units but it would be a waste because you will need a lot and most unit stacks have AA.For example you will need 7 flying bombs to take out a 3 stack of one AC and two Infantry(tried and tested)
