Be careful, I think you need something like 50-60GB of free space to run it. And the script does not check the free space beforehand.
After the script is run, I think the OS X VM will occupy at least 25GB.
PS: the graphics performance is ok, but not great. I could not manage to install the extension package of VirtualBox, so may be if you can install it, then the graphics performance of the virtualized OSX will improve.