Shaking a controller to break free from an enemy's grasp has been commonplace since developers started shoehorning it into Wii and PS3 games. ZombiU's "break free" function seems little different, and I can't affirm or refute that, since I was so liberal with my shotgun headshots during the demo that no zombie ever got close to me.
To be fair, I was probably playing on the easiest setting. And there were a few times when it did come pretty close, like when I ran out of shotgun ammo and had to switch back to the pistol on the fly. I forgot where to look (a problem that will hopefully be alleviated as we get used to the tablet screen) and gave a zombie an opportunity to close in. Luckily, I had a melee weapon and switched to it without further delay.