This plugin has a decent set of features, but the admin area is just not intuitive at all. The settings are dispersed in various different places, and setting up items with multiple options requires 3-5 clicks into completely different areas you really wouldn't think to look unless you read their instructions thoroughly.
I ended up going with WooCommerce and found it to be much easier to work with, less time spent reading on how to make it work, and quicker to get it up and working for my short deadline.
I think this plugin could be great, but it definitely needs a person with a usability background to help these guys out. :)