This AA now has many ranks. It is good. Get it. It really doesn't matter what class you have that it is available for, it gives you more attacks. Additional ranks give you an increased chance to flurry. As a level 85 Warrior, I flurry anywhere from 5-10 times a fight, depending on the duration of the encounter. It would be far more against a tough raid monster. Each flurry, as far as I have observed, IS two additional attacks, not up to two. So, simple math says that I gain an additional 10-20 attacks per fight that I normally wouldn't have had. At an average hit of, say, 500 damage, and assuming all of them hit, that's 5k-10k more damage that fight. For everyone that is good. For tank classes, it's even better, since a great deal of our threat generation (Warriors especially) comes from damage and attacks. I seperate these because you can proc on misses, and there are some pretty sweet hate procs out there. More attacks mean a greater chance for these to occur, which makes this little Warrior feel warm inside.
I hope this helps.