Possibility of resolve reviewer Calendar Permissions as in Outlook
I already did a request on this topic and your support suggested to do a feature request. The problem is that as long as you have the reviewer permission on another calendar you can see the subject and location of private appointments (its a"tag" when creating appointments and it gets an lock icon). in the Sophos Secure Email app. If you change the permission from Reviewer to Free/Busy (both are preset permissions in Exchange/Outlook) you can't see the Subject and Location anymore.
In Outlook there is no possibility to view the details of other peoples calendars.
In conclusion calendar permissions are working differently in your email app than in Outlook