the only downside of sync utilities, assuming you send files over a local network,
it that you may need to grant some remote write permissions to the calibre folders so that the sync utilitiy can do its thing.
Not a huge security risk but something you will have to enable IF you run the utility from desktop had ask it to push the changes to laptop. Less so if you run it on the laptop and have it pull the changes from the desktop source. I have done stuff in that latter manner with free file sync, which will grumble about not being able to file lock the remote files that it is reading, while it reads them, but will will work
Whatever you do, be clear your mind and in your settings which is the source and which is the mirror, for a one way sync, especially if the mirroring operation is set to delete any files no longer found on source.
if both PCs run windows, then setting up a homegroup for documents is one possible secure way to do the needed file permissions, but I don't use homegroup - don't even know if windows still promote it. I do know that my LAN permissions tend to get messed up by each big windows update and have to be enabled all over again for me to be able to move/copy my files & folders
As an aside, I did find an android app that will do a folder sync, reading from a shared LAN folder on a PC , or a cloud folder, and writing to the android device. so you could mantain a calibre mirror library on a tablet or phone. It is called foldersync and comes in free and pro versions from google store. The pro version allows filters so e.g. I could mirror only the epub section of my calibre library.