Recs.
Updated
Specs
Pros
Pro Easy to set up
Watson is a bit of a one stop shop for tone analysis. It's packages are self contained, so setup is simple and can be injected into nearly any app.
There aren't any dependencies and setup can be done via the command line by simply setting up an endpoint and a user engagement point. All setup steps are well documented here.
Pro Globally used with a good community
Watson is one of the more common tone analyzers and is used worldwide. The community surrounding it is fairly large, so any questions you have can be directed to an educated userbase. You can find Watson developers on StackExchange, the IBM forums, and they even have a Slack channel.
Cons
Con Limited non-English support
Some users have reported that Watson has trouble with other languages. Watson only officially supports English and French, so its support for other languages can be limited. Users have reported trouble with the Spanish tool specifically, saying that it's slow and unresponsive.