Disadvantages of the FAKA
The combination of FAT and KA does have a cost. It's hard to build, and unstable to operate. In the simplest setup, there is nothing designed to absorb energy, and it can not swing back and forth like most trebuchets until it stops. The leftover energy goes into battering the axle trucks into the stops, and the hanger into the upper arm stop. Of course, when properly tuned, there is very little energy left (The FAKA can be tuned for very high efficiency), but before its tuned, or in the event of a misfire things can go quite wrong. I have had several arm derailments.
My FAKA has misfired once, and it lead to the wheels smashing into the front stop and derailing the arm. This was with 5 pounds of CW. It has derailed several other times, but so far no major damage has occurred.
Also, the Golf Ball Beast lifts the back of the frame just before the arm is released. This is bad because it adds stress to the frame when it re-contacts the ground, and could (And I think it did) derail the axle.