Jack has already listed all of the pros of the product. A few other pros and cons about FreeFileSync, and some comparisons with SyncToy. We had to look into a solution for our laptops a few months ago and so I had done some research on this (we ended up selecting FreeFileSync for our needs):

Pros:
1. The FreeFileSync author is very responsive to problems and questions. I once had a minor issue that I found, and the author released a beta version within a few hours, and a production version within a day.
2. This project is still in active development (SyncToy has not had an update in quite some time).
3. I was able to create a config file that used variables in it that I was able to use for ALL of my userbase. While SyncToy does some command line parameters, it does not for instance allow you to exclude specific folders with the command line (we can exclude specific files via the command line though).
4. Since we can use a common shared config file for FreeFileSync, it is also easy to push new exceptions/changes to the config file if needed. To do this via the command line, SyncToy would require you to recreate the folder pair (or manually edit the existing folder pair via the GUI).
5. Good logging - FreeFileSync records what new files were added, removed and changed. We had found a bug in SyncToy that if it is run from the command line, i.e. the GUI is not used, the log file does not store what files were added/removed. From a troubleshooting perspective, this was important for us.

Cons:
1. FreeFileSync does NOT sync the folder timestamp (note that it DOES sync the file timestamps though - just the folders are ignored). Unfortunately, the developer feels that this is not important nor reliable to sync and does not have any plans to implement this. I don't have a link for this right now, but for some of my scenarios, this is one reason why I can't use FreeFileSync. This is my only real problem with FreeFileSync. It's minor for most scenarios, but can be important depending on what the sync is intended for.