Considering the fact that it has lots of functionality, it is a wonder how it seems to produce no errors for the user. I purchased the enterprise version and have had no regrets.
In my case I for example needed to give some not so skilful users the option to send newsletters from the front-end, and it was very easy and convenient to achieve this. Making templates and setting up default options for other users has been made easy for the admin.
There are many wonderful and neat features such as the option to check whether the mail about to be sent looks like spam. Also the way the administrator can check the general statistics the user history on clicks and opens is well implemented. More functionality seems to be coming all the time.
I must admit though that I have been using this extension for about two years, and there have been so many new features that I am not sure how easy it is to start using it from the beginning now. But I guess if you want totally simple newsletter system, there are ones with lesser options as well. But I would still encourage to give it a try with this one.
In case of problems, the developers have been very helpful.
I warmly recommend.