The ease of use to pull relevant data into an email with just one click! I LOVE IT. We've been using it since Day 1 (almost). Nothing so far. It's actually pretty great though - simple tool set up and easy access from anywhere in your inboxes at any time if you need help or have questions about how this fits within Marketing Automation / Salesforce as we're integrating both programs now. This has helped us gather more detailed information regarding prospect interest levels before outreach vs getting feedback/opinions via survey only after contact. And there are no regrets here either :) There isn't much downside but maybe some overhead cost associated? Not sure yet what those would be like exactly. You should definitely give these guys a shot because they really do listen & work hard towards providing their customers' needs first while still keeping everything fairly transparently priced without overcharging them.