Thanks for your interest in EasyRotator, and I'm sorry it didn't meet your needs.
The external editor application allows for more efficient and powerful editing features; for example, images can be resized and optimized before being uploaded to the web. Obviously, not every plugin is perfect for every use case. EasyRotator for WordPress is well maintained and offers extensive functionality. Many other plugins are more limited and/or don't receive regular maintenance. While the up-front setup usually takes a minute or two (definitely not as long as you experienced), we believe that the long-term benefits outweigh the initial investment.
You are correct that OS X and Windows are the two currently-supported platforms for creating and editing rotators. The rotators created with the plugin can be viewed on any platform and device.
Again, I'm sorry that EasyRotator didn't meet your needs. Please let me know if I may provide any additional assistance.