I am using Hiro for my Salesforce Marketing Cloud campaigns, it helped me to build more targeted lists of contacts who are interested in specific products or services that i offer from time to time. It has been very easy to setup up so far by just copying & pasting some code into SFMC automation editor which was super simple! The only thing they could improve would be making this an add-on option rather than pay per use as currently its quite costly when you consider how many data sources we require. We have successfully used Hiro to send bulk emails out at scale without having any issues thus far.