Homey Keynote

The data transferred between Homey Cloud and your home should be limited to the data that is going to and from the bridge antenna’s, plus your app usage. All the rest is cloud to cloud communication.

The amount of data a cloud to cloud connection will indirectly trigger due to communication with other bridges in your home will be hard to tell. It might be similar if that bridge retains its state in the cloud. If it doesn’t and if that state needs to be periodically polled then the amount of data will increase significantly. But I guess Athom will frown upon apps that rely on polling.