Yes, very safe!
When you share reports using the 'Share reports' button, each person that has been assessed is sent an email that contains a link to download their own 360 feedback report.
When a user accesses the download link, Spidergap marks that the report has been downloaded and prevents someone from reaccessing the URL. This is to prevent the report accidentally being shared when people forward on or reply-to the email with the link to download the report.
The report can take a few seconds to download so please be patient.