This set is amazing. The "A" variant is able to use Power Functions to use all of it's features, which allow you to turn the rotors, use the winch, raise and lower the wheels, and raise and lower the back ramp. To be honest, I was quite surprised that the set chose to put the raise/lower landing gear and turn rotors functions on the same gear, meaning that you can spin the rotors, raise the landing gear, but not do both at the same time. This is just personal preference, and I think that this is a great set with inventive features. Additionally, the set comes with the ability to change the angle of the rotor, an important part of flying a real helicopter.
The "B" variant, in my opinion, is the unsung hero of this set (there is a surprising lack of pics aside from Reveoon's, so I included some). With all Technic sets (that I can recall right now), the set comes with an "a" and "B" variant. The "A" variant is the set's original design. The "B" variant is Lego telling it's engineers to make something new and relative using only the parts given for the "A" variant. Many say the Technic and Creator sets are the same in this respect but in fact the Creator designers are allowed to use extra pieces for the additional models, whereas the Technic designers have a much tougher job with their much tighter parts supply. Nonetheless, the designers whipped up a truly amazing twin-rotor helicopter, which is a difficult design is you have access to as many pieces as you want. Limit the parts and create a complex and realistic design? I really don't know how the set designers did it.
I love the B variant more because of that ingenuity and the fact that you rarely see twin-rotor helicopters. The B variant comes with two of the four main features: the rotor turning and the landing gear (which once again cannot be done simultaneously). I love the landing gear design on the twin-rotor: two gears that come off of the sides of the helicopter and fold under the belly. Additionally the B variant allows the user to tilt the rotors just as the A variant does. Still really enjoy this set, was worth every penny! Definitely recommend if you find a used one for sale.
P.S. I didn't really think about this until the end of my review, but this set is H-U-G-E HUGE!!! That was my first impression of the set was wow this is big!! Huge set, huge rotor span, long helicopter, h-u-g-e!!