The plugin does work. There are 8 other merchants where it works fine, 4 of them are using it on their live website for more than 9 months already. The initial configuration can be a bit cumbersome if you aren't comfortable setting up cronjobs and editing the wp-config.php, but it will definitely work if everything is set up correctly.

I am happy to help you setting it up and sent you some instructions on how to create debug info and logfiles so we can find the issue.