The compression will probably be pretty good, we do not do any compression during the backup process. Try zipping it and find out.
Also, keep in mind that your MoH files are also backed up, so if you have a bunch of MoH files, and each one encoded in all the formats, this can add up very quickly. Try to restrict the MoH supported Codecs to the ones you actually use (typically 729 and 711u), and remove the unused sources.
