Seen quite a few times (NLP web APIs), and my opinion is that this kind of stuff tends to not be scalable: to be useful, such web APIs have to be able to do entire articles in just a split fraction of a second. Although I am not sure (because of the HN storm the API is down), it does not seem this tool will live up to those expectations, either. In the end, my choice always has been to include/wrap an off-the-shelf tool in your own pipeline rather than relying on a external service that might be too slow for end-users and mass mining alike...