Has anyone enabled "iCloud Music Library"? I'm curious to try it, because it's required in order to save Apple Music songs for offline listening, but I'm hesita

Has anyone enabled "iCloud Music Library"? I'm curious to try it, because it's required in order to save Apple Music songs for offline listening, but I'm hesitant because there seems to be insufficient description of the options to "merge" or "replace" the songs on my current device.