I own both. Both are good. I don't like the way that either connects to the Kapex...the Fastcap, less. Festool should incorporate the way that the Kapex hold-down clamps work and translate that concept to the connecting mechanism...Push wing up to the Kapex and flip the latch. Done! Simple, faster, better! No bending down looking, twisting and turning.
That said, the Festool wings are faster to set up and I like the internal extender. They are calibrated very well. Very accurate! The Fastcap wings are more robust, have standard and metric tape with a clever magnifier.
You have to figure out how you will be using your Kapex and buy the system which works the best for your situation. If you're working in small rooms, then the Festool is better. If you're at a site for an extended amount of time, cutting a lot of heavy product, and have a bunch of knuckle-heads bumping into things, then I would go with the Fastcap. If someone fell into the Festool wings, they would bend them up or break them. If someone fell into the Fastcap wings, then I don't think that there would be much damage if any at all.
