This is a really cool idea, there are other products out there that do the same thing, but there is definitely room to differentiate yourself.

One interesting issue, you might need to read the context a bit more to gauge if the post is actually talking about the Brand. For example Target is a common english word, and if you look at the results, only 1 usage was actually referring to the store Target.

One nice bonus that would be useful, I'd like to be able to compare sentiment by Subreddit, if i'm marketing on Reddit I would not target "Reddit" as a whole.