I've got the BT150 which is basically the same as the 100, it just has the digital bit on it which shows the room temp etc.
They are great !! We get crystal clear sound on them & they are sensitive enough that we can even hear DS2 breathing on them !! The monitor is on top of his wardrobe too, so it's not even like it is right next to him & we still hear every movement.
TBH I have not had to use the music, but its a great idea.