This is starting to look like a really great plugin. It can be used as a Booking form for Courses on your site, or, by changing the settings of the activity, for booking face-to-face workshops for example.  After installing (which was flawless) and testing we've found it to be reliable and stable.  There are some areas that can be improved, such as adding contextual help icons with clear descriptions of functionality.  Also, it's not totally clear how much 'manual control' there is for the book...