Despite MANY searches, I can't find a comparison of the GPL and Professional versions. Is there one I've missed?
I don't remember seeing a comparison table for GPL and Pro versions. But I seem to recall a comparison table for Virtualmin and cPanel etc.
The main difference between Virtualmin GPL and Pro is that with the Pro version, you get more timely updates and patches. Also, the user interface of the Pro version is a lot easier to use. In terms of underlying functionality, only Joe and Jamie can answer you in any detail.
You also get a much easier set up for the Pro version. With the Pro version, you don't really have to do anything except run the script.
I know when I installed the gpl version, there was a lot of stuff I had to learn to do and decisions to make.