all us equity and option data. nbbo for options. all equity data (regional and nbbo). Their technology allows for many symbols (about 1 million +).
I use to get imbalance data from them years ago when it was part of the regular NYSE feed but don't anymore. They likely don't have access to that info today (you should ask).
one of the great things is that you can re-run the tape each day. They also have some apps that they provide (like t&s and hot lists etc).
I also subscribe to another vendor (Thomson Reuters) for the things that NxCore doesn't have that I want. Symbology at T/R is limited to a few thousand symbols for the product I subscribe too.
IMO, you subscribe to NxCore for primary US data. Not for news/charts and some of the secondary types of data (like dividend/imbalance etc). They might still have some of this but you will likely be disappointed.
hope this helps.