It offers the service in variety of flavours like getting gender based on first name,last name and by email address. You can also include meta data like country and ip address for further refinement of the results. The probability score can be used from the response to reject or accept the results. Works great for data where this piece of information is missing. Review collected by and hosted on G2.com.

Other than filling out missing data details I don't find any specific use case of this API. Maybe they can add some more insights about the person which might be meaningfull in other scenarios as most of the web forms include gender option so 9/10 times this information is already available with data collectors and researchers Review collected by and hosted on G2.com.