Greetings!

I've just tried this addon for the first time. Nothing seems to work. I see the "Hide EFM" button on the map but it does does nothing, and when I visit a flight master it does only show known flight masters, like usual.

I'm using several addons so I'm not sure if this is an incompatibility or other issue.

First step to check for addon incompatibility, is to disable the other addons and see which one(s) cause the issue.

Alternatively, perhaps you are missing the fact that EFM does not come with data preloaded? You either need to decide to utilize the (currently incomplete) data set, or visit the flight masters yourself and it will learn the locations and times for flights itself. It should also be noted that the only change to the Blizzard flightmaster window that EFM does is add "time to fly" to the nodes as you mouse over them, which it can only do from either of the two things previously mentioned.