Here we go. http://davebunkerguitars.com/tf_neck.html In a nutshell, the tension from the headstock is isolated from the neck, it travels down the internal rod/channel/bar which is anchored to the body at the heel. It basically allows the neck and fretboard to have no tension or compression on it and resonate freely ( i think that's the theory). It's a very different way of building a neck and undoubtedly will have an effect on the sound-the consensus on the henbevs though is that they sound bloody excellent!
I had one here for a while.
The S2 is a great looking and playing guitar. It has a very immediate attack due to the tension free neck.
I loved the way it sounded too and the bigsby worked well with the locking tuners.
For me the only draw back was that the neck profile was too slim for me and the body a bit heavier than I normally would favor.
I hear that they are going to offer a bigger neck profile in the future.