They have many models of them, some that are small 4x6 size, and is just a blank slate style tablet, and then they have the real size 1:1 touch screen models. I learned on the cheaper 4x6 model and while i think the ones with the touchscreen would be nice to have, never felt a need to invest in one.
Biggest thing is, at leas to me, based on what i saw when i was in school for graphics design, the people who could draw tended to adapt to the wacom's much faster then those who could not draw, we had 4 people, myself included, who could draw, and we jumped ahead pretty fast over the ones that had to both learn to draw and learn to use the tablet.
It does take some getting used to though, cause you no longer are looking at your hand while you draw. A tip our instructor gave us was, she made a series of images and scaled them for print to fit the tablet size we had, so you could see the image on the screen and on the tablet, and told everyone to trace them onto a new layer in photoshop, it was a muscle memory building exercise.