I've been using this plugin successfully for a few weeks now. I'm happy with it. (I'm on Win7 Pro, with Outlook 2010.)
For anyone else coming to this thread while considering this plugin, here are a few more tidbits I learned that may help:
* n5bb/Bill links above to the Sourceforge page for the plugin, but from there you can find the link to the main project website, which includes good documentation, install notes, changelog, etc. Actually, here it is:
https://CalDAVsynchronizer.org/
* n5bb/Bill specifies above a type of 1-way sync. For my needs, I've been successfully using the 2-way/bidirectional sync option.
* In addition to the required minimum .NET Framework being installed (4.6.2 may be minimum), there's also the requirement of MS Visual Studio 2010 Tools for Office Runtime. I'm running v10.0.60828, which is above the minimum required. I downloaded it from the MS site somewhere.
* I heavily use the notes/comments field of calendar invites, including deep rich text formatting. I knew going into this that FastMail seems to only support plain text for the comments field. The plugin appears to cleanly strip out formatting and distill content down to plain text after syncing (and also spell out any embedded hyperlinks).
* I use category colors for my events in Outlook. Colors don't appear in the FastMail calendar, but even after remote editing of events from within FastMail, the event category colors back in Outlook seem to remain intact after syncing back to Outlook. (There is some potential customization of color mapping in the docs and advanced settings that I did not explore.)
That's about it. This is a nice handy tool.
-DG