Well, maybe the demo site needs attention but I have to say that the plugin works quite well and the developer is actually one of the most responsive I have dealt with. Very active, posts replies on the support forum regularly, and point upgrades and bug fixes have been frequent.
The documentation may be a bit thin, but between FWS and Zingiri posts on the net, some configuration settings trial and error, and a little code review you can usually get a question answered.
What I like about the plugin is that it is a lot simpler than some of the other open source ecommerce solutions out there. If you don't need the depth of Magento, this is a great choice.