v5.15 is easier to assemble, more robust, and (I hope) better documented. The zip file contains documentation in DocuBricks format, along with the STL files you need. To view this documentation, unzip the release and open the .xml file in a web browser (Firefox and Safari both work, we're not sure about Internet Explorer or Chrome).
The source code link provided by GitHub contains the original SCAD files and more STLs generated during development - please make sure to read the documentation before printing, and don't just print the contents of the STL folder. You need multiple copies of some parts and other parts are optional.
Since rc1 this version has better instructions and an improved illumination arm.