The site Wacom Business Solutions dedicated to the digital signing, which includes mostly everything about the STU, has been revamped for the launch of two new models (the both smalll tablets in the top right of the picture below): STU 430 and STU 530. One can easily guess that this is the same tablet, but one is in B & W and the other in color.
If you want more information about STU, click on the links of Wacometemapomme (it’s in french, but you can find the same informations in english. The first time we talk about this, it was in 2008 ( link ).
Wacom Business Soluyion is not only a tablet to sign, you get a plugin for PDF too. See video below