I like that it is easy to use as well as being able to monitor multiple sources of information at once so we can see what has been going on in our newsroom or with clients' websites etc.
It also allows us to archive content which makes finding old pieces easier. The only issue i have had was when trying to add new sites but this could be because my internet connection wasn't working properly during initial setup - however support were very helpful and resolved quickly! We are using NMs mainly within an internal team environment (ie not external customers) where they help give quick updates/alerts if something important happens across different platforms such as social networks, blogs etc.