Let’s say that I have a Public account on Prezi. My friend, who has a Pro account, sends me a PEZ file via email and my license does not include Desktop. Yes, I know there is a trial version of Desktop, but I don’t want a trial. I just want a simple PEZ viewer.
Your friend could send you a secure link to view it online, or the stand-alone viewer. The latter is quite big for email, yes, but if the viewer uses Windows, the whole prezi.app sub folder (usually ~80% of the .zip size) can be removed. That is just necessary for viewing on Mac OSX.
Or you could open the pez file with e.g. 7z, extract the content (content.xml and the repo folder), and paste it over the content.xml and the repo folder of an earlier extracted prezi you e.g. downloaded yourself in zip format of a standalone prezi.
Allthough I have not tried this myself, I am falry sure this will work.
On the other hand, a separate viewer for the desktop would not be that bad ;-0
(Fellow user, not affiliated with the prezi team).
What if that happened to me? I am a Mac user myself. Yes, I can try to use Wine to run it, but for Mac it requires you to compile it.