After installing Mailster I was able to set it up and get it working and from appearances it looked like exactly what I was looking for for a mail list component. Then I tried to backup my site with Akeeba. I had done due diligence and backed it up immediately before installing Mailster with no problem. After Mailster it failed with an indeterminate AJAX error right about the time the status bar was getting alphabetically to the Mailster component. I uninstalled Mailster and tried again and the backup succeeded without any errors as usual. I've been using Akeeba with great success for a long time now so I'm not willing to give it up for mailster, and Akeeba's support basically says poorly written components will result in AJAX errors. I wouldn't go that far, this looks like a good component with a lot of great features that might just still have a few bugs to work out. I could try just excluding the Mailster component directory from Akeeba and rolling like that, but I think I'll wait for future revisions before trying it out again... and if it works without a hitch in the future I'll update my rating here.
Thank you for your review.
We are of course always interested in improving Mailster. As we have problems reproducing the issue you describe we would be glad if you can contact us (please use the contact form on our site) so that you can help us identify the root cause. Thanks!