This app can only control media playback of other apps, it is not a media player itself. For this to work, Android mandates holding the permission to access notifications. The permission is only used to enable media controls. Notifications are not accessed in any way through this permission.
This feature helps you to see the screen a bit clearly while on the go. The image on the screen is stabilized by applying rapid small movements that try to counteract external shaking.
To save battery and data, only one elevation point will be acquired from the Internet when you start tracking a new track. This is enough for the rest of the track to have a more accurate altitude baseline.