The best thing about warm gun is its ease of use, it's quick to set up your first campaign, easy customization options which makes me feel more confident in my work than other tools I've used before (Outlook). Not much! It has all you need but if there was anything missing then i would say maybe some sorta stats or analytics section so we can see how our emails are performing overall as well as each individual segment etc? We're using this tool at @TheCrowdSourceProject as an additional way to communicate/engage users after they have submitted their feedback via social media channels such as Facebook & Instagram.