So, I got one of these. Foolishly, I bought mine from ebay, so my one has some problems outside of design (going to try returning it, since they make it v. unusable and it was advertised as 'as new').

But anyway, it gave me a chance to try out the device itself. And dear god, it's not worth it. It's basically a cute executive's toy for taking notes, not a tool for artists. I found that it frequently misread what I'd drawn, resulting in sloppy, scrawled versions of my sketches coming out in the program, which look noticably worse than the biro drawing that had resulted on the sheet. Sharp points are often lost and read as rounded curves, wiggles and spikes emerge where they shouldn't, etc.

Overall, not worth it unless you want very rough versions of your sketches to be vectorised on the go.