Posted on May 30, 2016.
In the gun world, there are a lot of things they people want "just in case" but don't even really need. These feel good features are typically, nice to have, but wholly unneccessary. Anti-rotation features on free floating rail systems are one of these unneeded features.
Having installed hundreds of rails, and inspected dozens of different rail systems, I firmly believe that anti-rotation features are a feel good measure at best, and a bandage on a bullet wound at worst. Anti-rotation features which stop rails from rotating typically are fairly small, and make use of the aluminum rail's body (anti-rotation tabs of ledges) or the aluminum upper receiver (internal anti-rotation pins) to resist hypothetical rotational forces. The amount of force these small bits of aluminum can take... is fairly minimal. This is important, because the amount of force required to rotate or loosen a correctly installed barrel nut is substantial, 30 to 60 foot pounds on a secure upper receiver. In the real world, that type of force isolated on the barrel nut simply does not exist. A force that could cause a properly installed barrel nut to some loose on a independent rifle is strong enough to completely destroy the rifle and end user long before the barrel nut comes loose, ie, helicopter crashes, explosions... and even then, the barrel nut is usually still firmly attached to the upper.
The only time anti-rotation features are useful is when the barrel nut is loose... and while a loose barrel weapon will still function, its accuracy is going to be terrible and borderline useless. Yes, I've run into weapons with improperly installed barrel nuts at carbine classes before... and that is why I am paranoid about install barrels/rails correctly, with the correct tools.
There is no denying that anti-rotation features are "nice", but in truth they are redundant and completely unnecessary on correctly installed free floating handguards. As a result, I would not place "anti rotation" features as a high priority when shopping for rail systems. Ergonomics, functionality, design, strength, weight, and even aesthetics are all more important than anti-rotation features when shopping and ranking rail systems.