That is as good a way as any, and likely more tidy than others. The only issue is that the Guest will need to have some signpost or attractor to ensure they actually do go to that course to find the documents you really want them to look at. All you need do is to set Allow Guest access to "Yes" and all done.
Guest Access allows for Read Only access. They cannot engage any activity, AFAIK.
As far as security goes, if that is your main concern, an alternative can be to have on the same server as your Moodle, or in DropBox or Google Spaces or even OneDrive a separate folder that holds the files. All you need then is a prompt of some sort that will lead to the files. That way there is no opportunity for a Guest to compromise the security of your Moodle.
