make sure you view the entire thread - great support from the plugin author, committed to customer service. That's huge in my book!
I reviewed the code structure of this plugin. The code is not commented and lacks any docblocks that I could find in the 15+ files I reviewed. The code is also riddled with globals, which wouldn't be a huge problem if the code was commented properly, which would allow any modern IDE to follow the inheritance/types of the code.
There are also bugs that haven't been tested or caught, such as using undefined variables. For example, in (in plugin 3.6) the file /views/views.php line 103 has an undefined variable $msg that's being passed by reference, it should be initialized on line 102 as $msg = ''. Again, this would be helped by proper comments.
It also lacks the ability to use the WordPress API to add actions or filter content.
In the templates directory, there are 7 do_action calls: http://cl.circletr.ee/image/3u1y3L3E0L0o
Compare that to WooCommerce's 158: http://cl.circletr.ee/image/370X2I2J340d
--For example, it's very useful in WooCommerce to be able to add an action to a checkout page, and not have to copy/override an entire template. Why? Because when WooCommerce releases the next major release, it's very easy for them to keep a do_action() call in a template, and then restructure the entire page's DOM, without fear of breaking interoperability.