Hey guys so I've actually been doing research on this my past 3 years at UVM, and thought I might be of some assistance. I'm not the ACL guru or anything but I've done a lot of research on Ski injuries, I've collaborated with the Stowe based company Knee Binding, and I have worked on the rehab of two high level Freeski athletes.
So as it has already been said the FKS, and Tyrollia rotating binding do not lessen your risk for ACL injury in any way. This is because of two things the point of rotation in the heel and the locked heel rotation while the heel piece is down.
ACL injuries occur in a few different ways while skiing. The most common is "The Phantom Foot" mechanism. This occurs when you are attempting to get up while still moving after a fall, attempting to recover from an off balance position to the rear, and attempting to sit down after losing control. In this case your inside tail edge of your uphill ski catches and applies a twisting force to your knee. Another common way for your ACL to tear includes landing backseat on a jump. When your tails hit it creates a lever pushing your boots forward and causing a forward translation of the tibia on the femur.
This is why it is also important to have strong quad muscles. I can't stress biomechanics enough. Skiing is a tiring sport. The stronger your leg muscles are, the less fatigue you will experience. The majority of injuries occur at the end of the day when you are tired.
It is well supported that in a controlled environment the knee binding will decrease the risk for ACL tears due to it's 3rd dimension release. This means the binding releases medially (in) when it receives a medial force. This only protects you from the phantom foot mechanism. There is not any conclusive data for on snow testing.
Overall I think Knee Binding makes a great binding especially for those who have had prior knee injuries. There are some other cool features to knee bindings too. The binding has a separate 3rd din for the medial heel release, and it doesn't release laterally (out) at the heel. This way you are still able to hold your edge without worrying about pre-release. The mounting system is a floating system which avoids major changes in the ski's flex that is often caused by most binding systems (this is cool with today's rockers, and reverse cambers). Also the baseplate is the same width of ski boot soleplates. I don't know what all binding companies don't do this. I think the resulting edge control from the baseplate is actually noticeable.
If you plan on going huge and if you are the kind of person that doesn't ever want his bindings to release then these are probably not right for you. It's still a safety first ski binding.
I have a pair of the Carbon editions on my Line prophet 100s, my other skis are Scott P3s with Dynastar (look) PX12 bindings.
Do you think I'm wasting my time trying to find ways to make freeskiing safer? Do you guys care about this kind of product? Do you care about your safety? What do you think about a binding that has a max din of 12?