From the webpage:
Find journalists by what they tweet
Powered by all the tweets since 2006 from more than 1 million journalist & media outlets.
Search for relevant journalists
Search through 1 billion+ real-time and historical tweets (since 2006, when Twitter was born) from 1 million+ journalists and media outlets, to find out all the relevant media contacts that have talked about your product, your business, your competitors, or any other keywords in your industry.
Searches can be limited to tweets, journalists and outlets.
The advanced search interface looks useful:
If you are mining twitter for news sources, this could prove to be very useful.
With the caveat that news sources tend to be highly repetitive. If the New York Times says the OPM hack originated in China, a large number of news lemmings will repeat that without a word of doubt or criticism. Still amounts to one unknown source cited by the New York Times. No matter how many times it is repeated.