After installing the package the file '/boot/system/settings/freesynd/freesynd.ini' has to be edited to point it at the original game's data files.
Currently the binaries are only compatible with the original Syndicate data files, if you own Syndicate Plus (original + expansion) the data files have to be patched as described here: https://community.pcgamingwiki.com/files/file/1201-syndicate-plus-patch-for-freesynd