Pretty good, nearly great.

Does everything I need it to. The default scroll bar control is simple and elegant in design but can be easily altered with CSS (there is no back-end user interface which is fine for me).

Only three issues that make it 4 stars instead of 5:

1. Support for responsive design is poor. I had to make a few containing divs created by the plugin width:100% !important because their width seems to only be calculated on page load and not when the browser resizes. Height is also not updated when the window is resized. I can work with this but it isn’t ideal.
2. There is a brief flash of an unstyled scroll bar on page load before the plugin does its thing.
3. In Firefox, using the mouse wheel scrolls both the ScrollPane element and the page at the same time.