I've had the Best Fence for about a year and I'm pretty happy with it.
My one frustration with it is assembly. If you need to install/uninstall each time you use it that can be a little cumbersome.
The plastic block that attaches to the Kapex and receives the rail has some flex to it. Compound that with using a stand that you need to adjust to hold the off end and it can take a few minutes of fiddling to get it set/square.
I can see where the Festool version would have the advantage of quicker setup.
What I do like about the Best Fence vs the Festool fence (besides lower cost) is the scale and stop bar thing. I know the Festool version has the flags but the Fastcap setup seems to be a more positive stop, especially with wider pieces.
Short answer - works really well, just requires a little more setup than a Festool product would.