How much data does the Satcom Direct Router use?

ForeFlight can use 100MB/hour or more, mostly downloading weather data. There may be more or less data usage depending on what map layers are enabled, what regions you are viewing, and other actions performed within the app.

You can navigate to MORE >DEVICES > SATCOM DIRECT ROUTER to disallow ForeFlight from using the internet. When ForeFlight is disallowed from using the internet, you won't be able to download new weather data, but this will prevent 100MB/hour of data charges.