First and foremost - it is intuitive. As soon as I was setup with an account, I jumped right into the tool without any trouble. Of course the RedFlag team had scheduled a demo so I could quickly get up to speed, but it was so simple that I could navigate it right away.
Secondly - the flexibility is huge. Flexibility in a many ways! First the flexibility to shape recipient groups is huge. For example - are you targeting a particular geography? A particular region? An account team? A department? The list goes on. I use this tool for emergency response (hurricanes, tornadoes, wildfires, etc.), but it is an effective solution for any kind of broad communication needs. Second is the flexibility to distribute messages via several channels. Text, phone calls, e-mails, etc. - not everybody wants to receive communication in the same way, so this offers a solution for everyone.
Third - data and analytics are a biggie for me! Data - RedFlag syncs with my company's data system nightly, so I know