I like that it is easy to use, very customizable with lots of different modules available for you as well! It's not cheap compared other services out there but if your looking at just sending emails this might be worth checking into - otherwise have some more options in mind when making decisions regarding platforms/services etc before signing up (i'm sure they are great too!).
We've been able to send many campaigns throughout our business using charlie without any issues or complaints from clients so far!!