Rated 5 out of 5 stars
Excellent in every way - functionality, ease of use and documentation.
Been using it with Send Later extension once every month to send 500 to 700 customized emails for more than a year (non-profit purpose) and it has never failed, never crashed. It's actually a pleasure to see it working - merging, queuing and sending emails one by one in a very smooth fashion.
Big thanks to the developer for putting in the time and effort to develop and maintain it. The world is a better place because of people like you.
This extension deserves 10 stars out of 5.