Lukas,
The distinction is this: In the epic world, the initial action that is dispatched goes untouched through to the reducers first. Then the epics get triggered and the result of them dispatches new actions to the store that eventually go through all middleware again and down to reducers.
So with sagas and epics (redux-observable) you do not have an opportunity to influence the original action, you can only dispatch new actions.
With redux-logic you can intercept (allow, block, or modify) the original action in addition to being able to dispatch additional actions as the result of processing.
Thus you can design flows using additional actions to mimic similar use cases, but the number of actions is at least doubled. So in some situations it would be better to be able to intercept the original action altogether especially if you have a noisy store with lots of events.
Hopefully that helps to explain?
Jeff