As far as usability, at first I was a bit confused by how it worked with the layout and setting up of properties for forms, form elements etc.
I have seen a couple of the demonstration videos on the author's site and plan to return to watch others.
This gets a "good" rating (4 stars) due to my experience initially with the usability and "getting started" aspect, even though I figured it out in the end without any need for asking for support.
I tried to install the current version 1.7 in the stable Joomla 1.6 (January 2011 release) but it gives me PHP/database errors. No announcements (yet) on authors website either, about this.
Thanks for the comments. We have just released v1.8 beta of Freestyle Support which now supports Joomla 1.6. At the moment this is a beta version until we have had more feedback on the Joomla 1.6 site of thing to make sure they work ok.