I like how easy it is for me as developer (I'm not very tech savvy).
The UI makes sense even if its super simple! When sending out updates via email we could see in real time what percentage of people opened our emails vs clicked through them etc which was helpful when deciding where/how best spend resources with new features / bug fixes - so that's great too :) It took some getting used but once i did everything made more intuitive & easier than other platforms such as Salesforce CRM integration tools available from competitors e.g SFDC Lightning Connector API Integration Service by Appirio.