As discussed here and here, Outlook for Mac users cannot load any other Outlook user's calendar if the latter user's permissions are set to show "Free/Busy Only"; they can only load Outlook calendars whose permissions have been set to "Reviewer" (which I believe allows the viewer to see the event details).
This is really stupid, because (a) Outlook for Windows and Outlook Web Access users can load calendars with "Free/Busy Only" permissions without a problem, and (b) Outlook for Mac users can view other people's availability (at the free/busy level) by using the Meeting Scheduler tool. But this is a bad workaround because (a) it requires several non-intuitive steps in which you pretend to request a meeting and then cancel the invite, and (b) the Meeting Scheduler tool's graphical interface presents the invitee's calendar in a single one-dimensional line format that is almost unusable for looking over multiple days or weeks.
Is there a better workaround? The issue isn't that the viewer needs any additional availability information; they have all the information they need via the Meeting Scheduler, but it's presented in a virtually unreadable format. Is there some simple way to reshape that free/busy availability data into a readable 2D calendar format, as Outlook for Windows users can?