The Festool guides are placed off the workpiece, whereas most of the non-Festool guides go across the workpiece which helps to keep the guide rails steady. The weight of the Festool guides tips the guide rail sideways unless they are supported somehow.
The design of the Festool guides (using the narrow cut extensions) seems like it's better for narrow cuts that are smaller than the width of a guide rail. But, the extensions make supporting everything even more awkward because of the "bridge" that spans under the saw blade.
I have the Festool guides, but if I were buying today, and buying new, I'd probably go with a TSO set up.
There are some good videos in youtube from Festool and others showing the use of the Festool guides, and, as noted, several FOG threads as well.